diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index b0b014d598a..9546be1a27f 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -520,6 +520,11 @@ namespace ts {
             Strict,
         }
 
+        const enum MappedTypeModifiers {
+            Readonly = 1 << 0,
+            Optional = 1 << 1,
+        }
+
         const builtinGlobals = createSymbolTable();
         builtinGlobals.set(undefinedSymbol.escapedName, undefinedSymbol);
 
@@ -5866,6 +5871,17 @@ namespace ts {
             return type.modifiersType;
         }
 
+        function getMappedTypeModifiers(type: MappedType): MappedTypeModifiers {
+            return (type.declaration.readonlyToken ? MappedTypeModifiers.Readonly : 0) |
+                (type.declaration.questionToken ? MappedTypeModifiers.Optional : 0);
+        }
+
+        function getCombinedMappedTypeModifiers(type: MappedType): MappedTypeModifiers {
+            const modifiersType = getModifiersTypeFromMappedType(type);
+            return getMappedTypeModifiers(type) |
+                (isGenericMappedType(modifiersType) ? getMappedTypeModifiers(<MappedType>modifiersType) : 0);
+        }
+
         function isPartialMappedType(type: Type) {
             return getObjectFlags(type) & ObjectFlags.Mapped && !!(<MappedType>type).declaration.questionToken;
         }
@@ -9583,13 +9599,10 @@ namespace ts {
             // related to Y, where X' is an instantiation of X in which P is replaced with Q. Notice
             // that S and T are contra-variant whereas X and Y are co-variant.
             function mappedTypeRelatedTo(source: MappedType, target: MappedType, reportErrors: boolean): Ternary {
-                const sourceReadonly = !!source.declaration.readonlyToken;
-                const sourceOptional = !!source.declaration.questionToken;
-                const targetReadonly = !!target.declaration.readonlyToken;
-                const targetOptional = !!target.declaration.questionToken;
-                const modifiersRelated = relation === identityRelation ?
-                    sourceReadonly === targetReadonly && sourceOptional === targetOptional :
-                    relation === comparableRelation || !sourceOptional || targetOptional;
+                const modifiersRelated = relation === comparableRelation || (
+                    relation === identityRelation ? getMappedTypeModifiers(source) === getMappedTypeModifiers(target) :
+                        !(getCombinedMappedTypeModifiers(source) & MappedTypeModifiers.Optional) ||
+                        getCombinedMappedTypeModifiers(target) & MappedTypeModifiers.Optional);
                 if (modifiersRelated) {
                     let result: Ternary;
                     if (result = isRelatedTo(getConstraintTypeFromMappedType(<MappedType>target), getConstraintTypeFromMappedType(<MappedType>source), reportErrors)) {
diff --git a/tests/baselines/reference/mappedTypes5.errors.txt b/tests/baselines/reference/mappedTypes5.errors.txt
new file mode 100644
index 00000000000..d0c32cd1dd9
--- /dev/null
+++ b/tests/baselines/reference/mappedTypes5.errors.txt
@@ -0,0 +1,73 @@
+tests/cases/conformance/types/mapped/mappedTypes5.ts(6,9): error TS2322: Type 'Partial<T>' is not assignable to type 'Readonly<T>'.
+tests/cases/conformance/types/mapped/mappedTypes5.ts(8,9): error TS2322: Type 'Partial<Readonly<T>>' is not assignable to type 'Readonly<T>'.
+tests/cases/conformance/types/mapped/mappedTypes5.ts(9,9): error TS2322: Type 'Readonly<Partial<T>>' is not assignable to type 'Readonly<T>'.
+
+
+==== tests/cases/conformance/types/mapped/mappedTypes5.ts (3 errors) ====
+    function f<T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) {
+        let a1: Partial<T> = p;
+        let a2: Partial<T> = r;
+        let a3: Partial<T> = pr;
+        let a4: Partial<T> = rp;
+        let b1: Readonly<T> = p;  // Error
+            ~~
+!!! error TS2322: Type 'Partial<T>' is not assignable to type 'Readonly<T>'.
+        let b2: Readonly<T> = r;
+        let b3: Readonly<T> = pr;  // Error
+            ~~
+!!! error TS2322: Type 'Partial<Readonly<T>>' is not assignable to type 'Readonly<T>'.
+        let b4: Readonly<T> = rp;  // Error
+            ~~
+!!! error TS2322: Type 'Readonly<Partial<T>>' is not assignable to type 'Readonly<T>'.
+        let c1: Partial<Readonly<T>> = p;
+        let c2: Partial<Readonly<T>> = r;
+        let c3: Partial<Readonly<T>> = pr;
+        let c4: Partial<Readonly<T>> = rp;
+        let d1: Readonly<Partial<T>> = p;
+        let d2: Readonly<Partial<T>> = r;
+        let d3: Readonly<Partial<T>> = pr;
+        let d4: Readonly<Partial<T>> = rp;
+    }
+    
+    // Repro from #17682
+    
+    type State = {
+        [key: string]: string | boolean | number | null;
+    };
+    
+    type Args1<T extends State> = {
+        readonly previous: Readonly<Partial<T>>;
+        readonly current: Readonly<Partial<T>>;
+    };
+    
+    type Args2<T extends State> = {
+        readonly previous: Partial<Readonly<T>>;
+        readonly current: Partial<Readonly<T>>;
+    };
+    
+    function doit<T extends State>() {
+        let previous: Partial<T> = Object.create(null);
+        let current: Partial<T> = Object.create(null);
+        let args1: Args1<T> = { previous, current };
+        let args2: Args2<T> = { previous, current };
+    }
+    
+    type State2 = { foo: number, bar: string };
+    
+    type Args3 = {
+        readonly previous: Readonly<Partial<State2>>;
+        readonly current: Readonly<Partial<State2>>;
+    };
+    
+    type Args4 = {
+        readonly previous: Partial<Readonly<State2>>;
+        readonly current: Partial<Readonly<State2>>;
+    };
+    
+    function doit2() {
+        let previous: Partial<State2> = Object.create(null);
+        let current: Partial<State2> = Object.create(null);
+        let args1: Args3 = { previous, current };
+        let args2: Args4 = { previous, current };
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/mappedTypes5.js b/tests/baselines/reference/mappedTypes5.js
new file mode 100644
index 00000000000..6f20b71ed7b
--- /dev/null
+++ b/tests/baselines/reference/mappedTypes5.js
@@ -0,0 +1,95 @@
+//// [mappedTypes5.ts]
+function f<T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) {
+    let a1: Partial<T> = p;
+    let a2: Partial<T> = r;
+    let a3: Partial<T> = pr;
+    let a4: Partial<T> = rp;
+    let b1: Readonly<T> = p;  // Error
+    let b2: Readonly<T> = r;
+    let b3: Readonly<T> = pr;  // Error
+    let b4: Readonly<T> = rp;  // Error
+    let c1: Partial<Readonly<T>> = p;
+    let c2: Partial<Readonly<T>> = r;
+    let c3: Partial<Readonly<T>> = pr;
+    let c4: Partial<Readonly<T>> = rp;
+    let d1: Readonly<Partial<T>> = p;
+    let d2: Readonly<Partial<T>> = r;
+    let d3: Readonly<Partial<T>> = pr;
+    let d4: Readonly<Partial<T>> = rp;
+}
+
+// Repro from #17682
+
+type State = {
+    [key: string]: string | boolean | number | null;
+};
+
+type Args1<T extends State> = {
+    readonly previous: Readonly<Partial<T>>;
+    readonly current: Readonly<Partial<T>>;
+};
+
+type Args2<T extends State> = {
+    readonly previous: Partial<Readonly<T>>;
+    readonly current: Partial<Readonly<T>>;
+};
+
+function doit<T extends State>() {
+    let previous: Partial<T> = Object.create(null);
+    let current: Partial<T> = Object.create(null);
+    let args1: Args1<T> = { previous, current };
+    let args2: Args2<T> = { previous, current };
+}
+
+type State2 = { foo: number, bar: string };
+
+type Args3 = {
+    readonly previous: Readonly<Partial<State2>>;
+    readonly current: Readonly<Partial<State2>>;
+};
+
+type Args4 = {
+    readonly previous: Partial<Readonly<State2>>;
+    readonly current: Partial<Readonly<State2>>;
+};
+
+function doit2() {
+    let previous: Partial<State2> = Object.create(null);
+    let current: Partial<State2> = Object.create(null);
+    let args1: Args3 = { previous, current };
+    let args2: Args4 = { previous, current };
+}
+
+
+//// [mappedTypes5.js]
+"use strict";
+function f(p, r, pr, rp) {
+    var a1 = p;
+    var a2 = r;
+    var a3 = pr;
+    var a4 = rp;
+    var b1 = p; // Error
+    var b2 = r;
+    var b3 = pr; // Error
+    var b4 = rp; // Error
+    var c1 = p;
+    var c2 = r;
+    var c3 = pr;
+    var c4 = rp;
+    var d1 = p;
+    var d2 = r;
+    var d3 = pr;
+    var d4 = rp;
+}
+function doit() {
+    var previous = Object.create(null);
+    var current = Object.create(null);
+    var args1 = { previous: previous, current: current };
+    var args2 = { previous: previous, current: current };
+}
+function doit2() {
+    var previous = Object.create(null);
+    var current = Object.create(null);
+    var args1 = { previous: previous, current: current };
+    var args2 = { previous: previous, current: current };
+}
diff --git a/tests/baselines/reference/mappedTypes5.symbols b/tests/baselines/reference/mappedTypes5.symbols
new file mode 100644
index 00000000000..7a499c4c4e9
--- /dev/null
+++ b/tests/baselines/reference/mappedTypes5.symbols
@@ -0,0 +1,279 @@
+=== tests/cases/conformance/types/mapped/mappedTypes5.ts ===
+function f<T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) {
+>f : Symbol(f, Decl(mappedTypes5.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>p : Symbol(p, Decl(mappedTypes5.ts, 0, 14))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>r : Symbol(r, Decl(mappedTypes5.ts, 0, 28))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>pr : Symbol(pr, Decl(mappedTypes5.ts, 0, 44))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>rp : Symbol(rp, Decl(mappedTypes5.ts, 0, 70))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+
+    let a1: Partial<T> = p;
+>a1 : Symbol(a1, Decl(mappedTypes5.ts, 1, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>p : Symbol(p, Decl(mappedTypes5.ts, 0, 14))
+
+    let a2: Partial<T> = r;
+>a2 : Symbol(a2, Decl(mappedTypes5.ts, 2, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>r : Symbol(r, Decl(mappedTypes5.ts, 0, 28))
+
+    let a3: Partial<T> = pr;
+>a3 : Symbol(a3, Decl(mappedTypes5.ts, 3, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>pr : Symbol(pr, Decl(mappedTypes5.ts, 0, 44))
+
+    let a4: Partial<T> = rp;
+>a4 : Symbol(a4, Decl(mappedTypes5.ts, 4, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>rp : Symbol(rp, Decl(mappedTypes5.ts, 0, 70))
+
+    let b1: Readonly<T> = p;  // Error
+>b1 : Symbol(b1, Decl(mappedTypes5.ts, 5, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>p : Symbol(p, Decl(mappedTypes5.ts, 0, 14))
+
+    let b2: Readonly<T> = r;
+>b2 : Symbol(b2, Decl(mappedTypes5.ts, 6, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>r : Symbol(r, Decl(mappedTypes5.ts, 0, 28))
+
+    let b3: Readonly<T> = pr;  // Error
+>b3 : Symbol(b3, Decl(mappedTypes5.ts, 7, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>pr : Symbol(pr, Decl(mappedTypes5.ts, 0, 44))
+
+    let b4: Readonly<T> = rp;  // Error
+>b4 : Symbol(b4, Decl(mappedTypes5.ts, 8, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>rp : Symbol(rp, Decl(mappedTypes5.ts, 0, 70))
+
+    let c1: Partial<Readonly<T>> = p;
+>c1 : Symbol(c1, Decl(mappedTypes5.ts, 9, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>p : Symbol(p, Decl(mappedTypes5.ts, 0, 14))
+
+    let c2: Partial<Readonly<T>> = r;
+>c2 : Symbol(c2, Decl(mappedTypes5.ts, 10, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>r : Symbol(r, Decl(mappedTypes5.ts, 0, 28))
+
+    let c3: Partial<Readonly<T>> = pr;
+>c3 : Symbol(c3, Decl(mappedTypes5.ts, 11, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>pr : Symbol(pr, Decl(mappedTypes5.ts, 0, 44))
+
+    let c4: Partial<Readonly<T>> = rp;
+>c4 : Symbol(c4, Decl(mappedTypes5.ts, 12, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>rp : Symbol(rp, Decl(mappedTypes5.ts, 0, 70))
+
+    let d1: Readonly<Partial<T>> = p;
+>d1 : Symbol(d1, Decl(mappedTypes5.ts, 13, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>p : Symbol(p, Decl(mappedTypes5.ts, 0, 14))
+
+    let d2: Readonly<Partial<T>> = r;
+>d2 : Symbol(d2, Decl(mappedTypes5.ts, 14, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>r : Symbol(r, Decl(mappedTypes5.ts, 0, 28))
+
+    let d3: Readonly<Partial<T>> = pr;
+>d3 : Symbol(d3, Decl(mappedTypes5.ts, 15, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>pr : Symbol(pr, Decl(mappedTypes5.ts, 0, 44))
+
+    let d4: Readonly<Partial<T>> = rp;
+>d4 : Symbol(d4, Decl(mappedTypes5.ts, 16, 7))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 0, 11))
+>rp : Symbol(rp, Decl(mappedTypes5.ts, 0, 70))
+}
+
+// Repro from #17682
+
+type State = {
+>State : Symbol(State, Decl(mappedTypes5.ts, 17, 1))
+
+    [key: string]: string | boolean | number | null;
+>key : Symbol(key, Decl(mappedTypes5.ts, 22, 5))
+
+};
+
+type Args1<T extends State> = {
+>Args1 : Symbol(Args1, Decl(mappedTypes5.ts, 23, 2))
+>T : Symbol(T, Decl(mappedTypes5.ts, 25, 11))
+>State : Symbol(State, Decl(mappedTypes5.ts, 17, 1))
+
+    readonly previous: Readonly<Partial<T>>;
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 25, 31))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 25, 11))
+
+    readonly current: Readonly<Partial<T>>;
+>current : Symbol(current, Decl(mappedTypes5.ts, 26, 44))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 25, 11))
+
+};
+
+type Args2<T extends State> = {
+>Args2 : Symbol(Args2, Decl(mappedTypes5.ts, 28, 2))
+>T : Symbol(T, Decl(mappedTypes5.ts, 30, 11))
+>State : Symbol(State, Decl(mappedTypes5.ts, 17, 1))
+
+    readonly previous: Partial<Readonly<T>>;
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 30, 31))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 30, 11))
+
+    readonly current: Partial<Readonly<T>>;
+>current : Symbol(current, Decl(mappedTypes5.ts, 31, 44))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 30, 11))
+
+};
+
+function doit<T extends State>() {
+>doit : Symbol(doit, Decl(mappedTypes5.ts, 33, 2))
+>T : Symbol(T, Decl(mappedTypes5.ts, 35, 14))
+>State : Symbol(State, Decl(mappedTypes5.ts, 17, 1))
+
+    let previous: Partial<T> = Object.create(null);
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 36, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 35, 14))
+>Object.create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let current: Partial<T> = Object.create(null);
+>current : Symbol(current, Decl(mappedTypes5.ts, 37, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypes5.ts, 35, 14))
+>Object.create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let args1: Args1<T> = { previous, current };
+>args1 : Symbol(args1, Decl(mappedTypes5.ts, 38, 7))
+>Args1 : Symbol(Args1, Decl(mappedTypes5.ts, 23, 2))
+>T : Symbol(T, Decl(mappedTypes5.ts, 35, 14))
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 38, 27))
+>current : Symbol(current, Decl(mappedTypes5.ts, 38, 37))
+
+    let args2: Args2<T> = { previous, current };
+>args2 : Symbol(args2, Decl(mappedTypes5.ts, 39, 7))
+>Args2 : Symbol(Args2, Decl(mappedTypes5.ts, 28, 2))
+>T : Symbol(T, Decl(mappedTypes5.ts, 35, 14))
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 39, 27))
+>current : Symbol(current, Decl(mappedTypes5.ts, 39, 37))
+}
+
+type State2 = { foo: number, bar: string };
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+>foo : Symbol(foo, Decl(mappedTypes5.ts, 42, 15))
+>bar : Symbol(bar, Decl(mappedTypes5.ts, 42, 28))
+
+type Args3 = {
+>Args3 : Symbol(Args3, Decl(mappedTypes5.ts, 42, 43))
+
+    readonly previous: Readonly<Partial<State2>>;
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 44, 14))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+
+    readonly current: Readonly<Partial<State2>>;
+>current : Symbol(current, Decl(mappedTypes5.ts, 45, 49))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+
+};
+
+type Args4 = {
+>Args4 : Symbol(Args4, Decl(mappedTypes5.ts, 47, 2))
+
+    readonly previous: Partial<Readonly<State2>>;
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 49, 14))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+
+    readonly current: Partial<Readonly<State2>>;
+>current : Symbol(current, Decl(mappedTypes5.ts, 50, 49))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+
+};
+
+function doit2() {
+>doit2 : Symbol(doit2, Decl(mappedTypes5.ts, 52, 2))
+
+    let previous: Partial<State2> = Object.create(null);
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 55, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+>Object.create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let current: Partial<State2> = Object.create(null);
+>current : Symbol(current, Decl(mappedTypes5.ts, 56, 7))
+>Partial : Symbol(Partial, Decl(lib.d.ts, --, --))
+>State2 : Symbol(State2, Decl(mappedTypes5.ts, 40, 1))
+>Object.create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>create : Symbol(ObjectConstructor.create, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let args1: Args3 = { previous, current };
+>args1 : Symbol(args1, Decl(mappedTypes5.ts, 57, 7))
+>Args3 : Symbol(Args3, Decl(mappedTypes5.ts, 42, 43))
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 57, 24))
+>current : Symbol(current, Decl(mappedTypes5.ts, 57, 34))
+
+    let args2: Args4 = { previous, current };
+>args2 : Symbol(args2, Decl(mappedTypes5.ts, 58, 7))
+>Args4 : Symbol(Args4, Decl(mappedTypes5.ts, 47, 2))
+>previous : Symbol(previous, Decl(mappedTypes5.ts, 58, 24))
+>current : Symbol(current, Decl(mappedTypes5.ts, 58, 34))
+}
+
diff --git a/tests/baselines/reference/mappedTypes5.types b/tests/baselines/reference/mappedTypes5.types
new file mode 100644
index 00000000000..2cbc66523e2
--- /dev/null
+++ b/tests/baselines/reference/mappedTypes5.types
@@ -0,0 +1,292 @@
+=== tests/cases/conformance/types/mapped/mappedTypes5.ts ===
+function f<T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) {
+>f : <T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) => void
+>T : T
+>p : Partial<T>
+>Partial : Partial<T>
+>T : T
+>r : Readonly<T>
+>Readonly : Readonly<T>
+>T : T
+>pr : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>rp : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+
+    let a1: Partial<T> = p;
+>a1 : Partial<T>
+>Partial : Partial<T>
+>T : T
+>p : Partial<T>
+
+    let a2: Partial<T> = r;
+>a2 : Partial<T>
+>Partial : Partial<T>
+>T : T
+>r : Readonly<T>
+
+    let a3: Partial<T> = pr;
+>a3 : Partial<T>
+>Partial : Partial<T>
+>T : T
+>pr : Partial<Readonly<T>>
+
+    let a4: Partial<T> = rp;
+>a4 : Partial<T>
+>Partial : Partial<T>
+>T : T
+>rp : Readonly<Partial<T>>
+
+    let b1: Readonly<T> = p;  // Error
+>b1 : Readonly<T>
+>Readonly : Readonly<T>
+>T : T
+>p : Partial<T>
+
+    let b2: Readonly<T> = r;
+>b2 : Readonly<T>
+>Readonly : Readonly<T>
+>T : T
+>r : Readonly<T>
+
+    let b3: Readonly<T> = pr;  // Error
+>b3 : Readonly<T>
+>Readonly : Readonly<T>
+>T : T
+>pr : Partial<Readonly<T>>
+
+    let b4: Readonly<T> = rp;  // Error
+>b4 : Readonly<T>
+>Readonly : Readonly<T>
+>T : T
+>rp : Readonly<Partial<T>>
+
+    let c1: Partial<Readonly<T>> = p;
+>c1 : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>p : Partial<T>
+
+    let c2: Partial<Readonly<T>> = r;
+>c2 : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>r : Readonly<T>
+
+    let c3: Partial<Readonly<T>> = pr;
+>c3 : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>pr : Partial<Readonly<T>>
+
+    let c4: Partial<Readonly<T>> = rp;
+>c4 : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+>rp : Readonly<Partial<T>>
+
+    let d1: Readonly<Partial<T>> = p;
+>d1 : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+>p : Partial<T>
+
+    let d2: Readonly<Partial<T>> = r;
+>d2 : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+>r : Readonly<T>
+
+    let d3: Readonly<Partial<T>> = pr;
+>d3 : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+>pr : Partial<Readonly<T>>
+
+    let d4: Readonly<Partial<T>> = rp;
+>d4 : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+>rp : Readonly<Partial<T>>
+}
+
+// Repro from #17682
+
+type State = {
+>State : State
+
+    [key: string]: string | boolean | number | null;
+>key : string
+>null : null
+
+};
+
+type Args1<T extends State> = {
+>Args1 : Args1<T>
+>T : T
+>State : State
+
+    readonly previous: Readonly<Partial<T>>;
+>previous : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+
+    readonly current: Readonly<Partial<T>>;
+>current : Readonly<Partial<T>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>T : T
+
+};
+
+type Args2<T extends State> = {
+>Args2 : Args2<T>
+>T : T
+>State : State
+
+    readonly previous: Partial<Readonly<T>>;
+>previous : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+
+    readonly current: Partial<Readonly<T>>;
+>current : Partial<Readonly<T>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>T : T
+
+};
+
+function doit<T extends State>() {
+>doit : <T extends State>() => void
+>T : T
+>State : State
+
+    let previous: Partial<T> = Object.create(null);
+>previous : Partial<T>
+>Partial : Partial<T>
+>T : T
+>Object.create(null) : any
+>Object.create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>Object : ObjectConstructor
+>create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>null : null
+
+    let current: Partial<T> = Object.create(null);
+>current : Partial<T>
+>Partial : Partial<T>
+>T : T
+>Object.create(null) : any
+>Object.create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>Object : ObjectConstructor
+>create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>null : null
+
+    let args1: Args1<T> = { previous, current };
+>args1 : Args1<T>
+>Args1 : Args1<T>
+>T : T
+>{ previous, current } : { previous: Partial<T>; current: Partial<T>; }
+>previous : Partial<T>
+>current : Partial<T>
+
+    let args2: Args2<T> = { previous, current };
+>args2 : Args2<T>
+>Args2 : Args2<T>
+>T : T
+>{ previous, current } : { previous: Partial<T>; current: Partial<T>; }
+>previous : Partial<T>
+>current : Partial<T>
+}
+
+type State2 = { foo: number, bar: string };
+>State2 : State2
+>foo : number
+>bar : string
+
+type Args3 = {
+>Args3 : Args3
+
+    readonly previous: Readonly<Partial<State2>>;
+>previous : Readonly<Partial<State2>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>State2 : State2
+
+    readonly current: Readonly<Partial<State2>>;
+>current : Readonly<Partial<State2>>
+>Readonly : Readonly<T>
+>Partial : Partial<T>
+>State2 : State2
+
+};
+
+type Args4 = {
+>Args4 : Args4
+
+    readonly previous: Partial<Readonly<State2>>;
+>previous : Partial<Readonly<State2>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>State2 : State2
+
+    readonly current: Partial<Readonly<State2>>;
+>current : Partial<Readonly<State2>>
+>Partial : Partial<T>
+>Readonly : Readonly<T>
+>State2 : State2
+
+};
+
+function doit2() {
+>doit2 : () => void
+
+    let previous: Partial<State2> = Object.create(null);
+>previous : Partial<State2>
+>Partial : Partial<T>
+>State2 : State2
+>Object.create(null) : any
+>Object.create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>Object : ObjectConstructor
+>create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>null : null
+
+    let current: Partial<State2> = Object.create(null);
+>current : Partial<State2>
+>Partial : Partial<T>
+>State2 : State2
+>Object.create(null) : any
+>Object.create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>Object : ObjectConstructor
+>create : { (o: object | null): any; (o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any; }
+>null : null
+
+    let args1: Args3 = { previous, current };
+>args1 : Args3
+>Args3 : Args3
+>{ previous, current } : { previous: Partial<State2>; current: Partial<State2>; }
+>previous : Partial<State2>
+>current : Partial<State2>
+
+    let args2: Args4 = { previous, current };
+>args2 : Args4
+>Args4 : Args4
+>{ previous, current } : { previous: Partial<State2>; current: Partial<State2>; }
+>previous : Partial<State2>
+>current : Partial<State2>
+}
+
diff --git a/tests/cases/conformance/types/mapped/mappedTypes5.ts b/tests/cases/conformance/types/mapped/mappedTypes5.ts
new file mode 100644
index 00000000000..38a010da0f5
--- /dev/null
+++ b/tests/cases/conformance/types/mapped/mappedTypes5.ts
@@ -0,0 +1,62 @@
+// @strict: true
+
+function f<T>(p: Partial<T>, r: Readonly<T>, pr: Partial<Readonly<T>>, rp: Readonly<Partial<T>>) {
+    let a1: Partial<T> = p;
+    let a2: Partial<T> = r;
+    let a3: Partial<T> = pr;
+    let a4: Partial<T> = rp;
+    let b1: Readonly<T> = p;  // Error
+    let b2: Readonly<T> = r;
+    let b3: Readonly<T> = pr;  // Error
+    let b4: Readonly<T> = rp;  // Error
+    let c1: Partial<Readonly<T>> = p;
+    let c2: Partial<Readonly<T>> = r;
+    let c3: Partial<Readonly<T>> = pr;
+    let c4: Partial<Readonly<T>> = rp;
+    let d1: Readonly<Partial<T>> = p;
+    let d2: Readonly<Partial<T>> = r;
+    let d3: Readonly<Partial<T>> = pr;
+    let d4: Readonly<Partial<T>> = rp;
+}
+
+// Repro from #17682
+
+type State = {
+    [key: string]: string | boolean | number | null;
+};
+
+type Args1<T extends State> = {
+    readonly previous: Readonly<Partial<T>>;
+    readonly current: Readonly<Partial<T>>;
+};
+
+type Args2<T extends State> = {
+    readonly previous: Partial<Readonly<T>>;
+    readonly current: Partial<Readonly<T>>;
+};
+
+function doit<T extends State>() {
+    let previous: Partial<T> = Object.create(null);
+    let current: Partial<T> = Object.create(null);
+    let args1: Args1<T> = { previous, current };
+    let args2: Args2<T> = { previous, current };
+}
+
+type State2 = { foo: number, bar: string };
+
+type Args3 = {
+    readonly previous: Readonly<Partial<State2>>;
+    readonly current: Readonly<Partial<State2>>;
+};
+
+type Args4 = {
+    readonly previous: Partial<Readonly<State2>>;
+    readonly current: Partial<Readonly<State2>>;
+};
+
+function doit2() {
+    let previous: Partial<State2> = Object.create(null);
+    let current: Partial<State2> = Object.create(null);
+    let args1: Args3 = { previous, current };
+    let args2: Args4 = { previous, current };
+}