diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f4d8c99c471..01b3a047d1d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13048,7 +13048,7 @@ namespace ts {
                 node.parent.kind === SyntaxKind.NonNullExpression ||
                 declaration.kind === SyntaxKind.VariableDeclaration && (<VariableDeclaration>declaration).exclamationToken ||
                 declaration.flags & NodeFlags.Ambient;
-            const initialType = assumeInitialized ? (isParameter ? removeOptionalityFromDeclaredType(type, getRootDeclaration(declaration) as VariableLikeDeclaration) : type) :
+            const initialType = assumeInitialized ? (isParameter ? removeOptionalityFromDeclaredType(type, declaration as VariableLikeDeclaration) : type) :
                 type === autoType || type === autoArrayType ? undefinedType :
                     getOptionalType(type);
             const flowType = getFlowTypeOfReference(node, type, initialType, flowContainer, !assumeInitialized);
diff --git a/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.errors.txt b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.errors.txt
new file mode 100644
index 00000000000..b2fea589cb1
--- /dev/null
+++ b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.errors.txt
@@ -0,0 +1,92 @@
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(6,8): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(16,7): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(21,7): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(31,8): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(45,10): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts(53,11): error TS2345: Argument of type 'number | null' is not assignable to parameter of type 'number | undefined'.
+  Type 'null' is not assignable to type 'number | undefined'.
+
+
+==== tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts (6 errors) ====
+    // https://github.com/Microsoft/TypeScript/issues/17080
+    
+    declare function f(a:number,b:number): void;
+    
+    function func1( {a, b}: {a: number, b?: number} = {a: 1, b: 2} ) {
+      f(a, b)
+           ~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+      // error
+    }
+    
+    function func2( {a, b = 3}: {a: number, b?:number} = {a: 1,b: 2} ) {
+      f(a, b)
+      // no error
+    }
+    
+    function func3( {a, b}: {a: number, b?: number} = {a: 1} ) {
+      f(a,b)
+          ~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+      // error
+    }
+    
+    function func4( {a: {b, c}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+      f(b,c)
+          ~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+      // error
+    }
+    
+    function func5({a: {b, c = 4}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+      f(b, c)
+      // no error
+    }
+    
+    function func6( {a: {b, c} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1,c: 2}, d: 3} ) {
+      f(b, c)
+           ~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+      // error
+    }
+    
+    function func7( {a: {b, c = 6} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1, c: 2}, d: 3} ) {
+      f(b, c)
+      // no error
+    }
+    
+    interface Foo {
+      readonly bar?: number;
+    }
+    
+    function performFoo({ bar }: Foo = {}) {
+      useBar(bar);
+             ~~~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+    }
+    
+    declare function useBar(bar: number): void;
+    
+    performFoo();
+    
+    function performFoo2({ bar = null }: Foo = {}) {
+      useBar2(bar);
+              ~~~
+!!! error TS2345: Argument of type 'number | null' is not assignable to parameter of type 'number | undefined'.
+!!! error TS2345:   Type 'null' is not assignable to type 'number | undefined'.
+    }
+    
+    declare function useBar2(bar: number | undefined): void;
+    
+    performFoo2();
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.js b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.js
new file mode 100644
index 00000000000..642f00a4f50
--- /dev/null
+++ b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.js
@@ -0,0 +1,108 @@
+//// [optionalParameterInDestructuringWithInitializer.ts]
+// https://github.com/Microsoft/TypeScript/issues/17080
+
+declare function f(a:number,b:number): void;
+
+function func1( {a, b}: {a: number, b?: number} = {a: 1, b: 2} ) {
+  f(a, b)
+  // error
+}
+
+function func2( {a, b = 3}: {a: number, b?:number} = {a: 1,b: 2} ) {
+  f(a, b)
+  // no error
+}
+
+function func3( {a, b}: {a: number, b?: number} = {a: 1} ) {
+  f(a,b)
+  // error
+}
+
+function func4( {a: {b, c}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+  f(b,c)
+  // error
+}
+
+function func5({a: {b, c = 4}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+  f(b, c)
+  // no error
+}
+
+function func6( {a: {b, c} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1,c: 2}, d: 3} ) {
+  f(b, c)
+  // error
+}
+
+function func7( {a: {b, c = 6} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1, c: 2}, d: 3} ) {
+  f(b, c)
+  // no error
+}
+
+interface Foo {
+  readonly bar?: number;
+}
+
+function performFoo({ bar }: Foo = {}) {
+  useBar(bar);
+}
+
+declare function useBar(bar: number): void;
+
+performFoo();
+
+function performFoo2({ bar = null }: Foo = {}) {
+  useBar2(bar);
+}
+
+declare function useBar2(bar: number | undefined): void;
+
+performFoo2();
+
+
+//// [optionalParameterInDestructuringWithInitializer.js]
+// https://github.com/Microsoft/TypeScript/issues/17080
+function func1(_a) {
+    var _b = _a === void 0 ? { a: 1, b: 2 } : _a, a = _b.a, b = _b.b;
+    f(a, b);
+    // error
+}
+function func2(_a) {
+    var _b = _a === void 0 ? { a: 1, b: 2 } : _a, a = _b.a, _c = _b.b, b = _c === void 0 ? 3 : _c;
+    f(a, b);
+    // no error
+}
+function func3(_a) {
+    var _b = _a === void 0 ? { a: 1 } : _a, a = _b.a, b = _b.b;
+    f(a, b);
+    // error
+}
+function func4(_a) {
+    var _b = _a === void 0 ? { a: { b: 1, c: 2 }, d: 3 } : _a, _c = _b.a, b = _c.b, c = _c.c, d = _b.d;
+    f(b, c);
+    // error
+}
+function func5(_a) {
+    var _b = _a === void 0 ? { a: { b: 1, c: 2 }, d: 3 } : _a, _c = _b.a, b = _c.b, _d = _c.c, c = _d === void 0 ? 4 : _d, d = _b.d;
+    f(b, c);
+    // no error
+}
+function func6(_a) {
+    var _b = _a === void 0 ? { a: { b: 1, c: 2 }, d: 3 } : _a, _c = _b.a, _d = _c === void 0 ? { b: 4, c: 5 } : _c, b = _d.b, c = _d.c, d = _b.d;
+    f(b, c);
+    // error
+}
+function func7(_a) {
+    var _b = _a === void 0 ? { a: { b: 1, c: 2 }, d: 3 } : _a, _c = _b.a, _d = _c === void 0 ? { b: 4, c: 5 } : _c, b = _d.b, _e = _d.c, c = _e === void 0 ? 6 : _e, d = _b.d;
+    f(b, c);
+    // no error
+}
+function performFoo(_a) {
+    var bar = (_a === void 0 ? {} : _a).bar;
+    useBar(bar);
+}
+performFoo();
+function performFoo2(_a) {
+    var _b = (_a === void 0 ? {} : _a).bar, bar = _b === void 0 ? null : _b;
+    useBar2(bar);
+}
+performFoo2();
diff --git a/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.symbols b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.symbols
new file mode 100644
index 00000000000..6d4cf484d92
--- /dev/null
+++ b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.symbols
@@ -0,0 +1,195 @@
+=== tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts ===
+// https://github.com/Microsoft/TypeScript/issues/17080
+
+declare function f(a:number,b:number): void;
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 2, 19))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 2, 28))
+
+function func1( {a, b}: {a: number, b?: number} = {a: 1, b: 2} ) {
+>func1 : Symbol(func1, Decl(optionalParameterInDestructuringWithInitializer.ts, 2, 44))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 19))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 25))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 35))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 51))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 56))
+
+  f(a, b)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 4, 19))
+
+  // error
+}
+
+function func2( {a, b = 3}: {a: number, b?:number} = {a: 1,b: 2} ) {
+>func2 : Symbol(func2, Decl(optionalParameterInDestructuringWithInitializer.ts, 7, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 19))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 29))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 39))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 54))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 59))
+
+  f(a, b)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 9, 19))
+
+  // no error
+}
+
+function func3( {a, b}: {a: number, b?: number} = {a: 1} ) {
+>func3 : Symbol(func3, Decl(optionalParameterInDestructuringWithInitializer.ts, 12, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 19))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 25))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 35))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 51))
+
+  f(a,b)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 17))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 14, 19))
+
+  // error
+}
+
+function func4( {a: {b, c}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+>func4 : Symbol(func4, Decl(optionalParameterInDestructuringWithInitializer.ts, 17, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 33))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 23))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 27))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 33))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 37))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 47))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 59))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 73))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 77))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 82))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 88))
+
+  f(b,c)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 19, 23))
+
+  // error
+}
+
+function func5({a: {b, c = 4}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+>func5 : Symbol(func5, Decl(optionalParameterInDestructuringWithInitializer.ts, 22, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 36))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 20))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 22))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 30))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 36))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 40))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 50))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 62))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 76))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 80))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 85))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 91))
+
+  f(b, c)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 20))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 24, 22))
+
+  // no error
+}
+
+function func6( {a: {b, c} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1,c: 2}, d: 3} ) {
+>func6 : Symbol(func6, Decl(optionalParameterInDestructuringWithInitializer.ts, 27, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 48))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 23))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 30))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 35))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 42))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 48))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 52))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 62))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 75))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 90))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 94))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 99))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 105))
+
+  f(b, c)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 29, 23))
+
+  // error
+}
+
+function func7( {a: {b, c = 6} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1, c: 2}, d: 3} ) {
+>func7 : Symbol(func7, Decl(optionalParameterInDestructuringWithInitializer.ts, 32, 1))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 52))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 23))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 34))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 39))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 46))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 52))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 56))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 66))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 79))
+>a : Symbol(a, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 94))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 98))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 103))
+>d : Symbol(d, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 110))
+
+  f(b, c)
+>f : Symbol(f, Decl(optionalParameterInDestructuringWithInitializer.ts, 0, 0))
+>b : Symbol(b, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 21))
+>c : Symbol(c, Decl(optionalParameterInDestructuringWithInitializer.ts, 34, 23))
+
+  // no error
+}
+
+interface Foo {
+>Foo : Symbol(Foo, Decl(optionalParameterInDestructuringWithInitializer.ts, 37, 1))
+
+  readonly bar?: number;
+>bar : Symbol(Foo.bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 39, 15))
+}
+
+function performFoo({ bar }: Foo = {}) {
+>performFoo : Symbol(performFoo, Decl(optionalParameterInDestructuringWithInitializer.ts, 41, 1))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 43, 21))
+>Foo : Symbol(Foo, Decl(optionalParameterInDestructuringWithInitializer.ts, 37, 1))
+
+  useBar(bar);
+>useBar : Symbol(useBar, Decl(optionalParameterInDestructuringWithInitializer.ts, 45, 1))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 43, 21))
+}
+
+declare function useBar(bar: number): void;
+>useBar : Symbol(useBar, Decl(optionalParameterInDestructuringWithInitializer.ts, 45, 1))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 47, 24))
+
+performFoo();
+>performFoo : Symbol(performFoo, Decl(optionalParameterInDestructuringWithInitializer.ts, 41, 1))
+
+function performFoo2({ bar = null }: Foo = {}) {
+>performFoo2 : Symbol(performFoo2, Decl(optionalParameterInDestructuringWithInitializer.ts, 49, 13))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 51, 22))
+>Foo : Symbol(Foo, Decl(optionalParameterInDestructuringWithInitializer.ts, 37, 1))
+
+  useBar2(bar);
+>useBar2 : Symbol(useBar2, Decl(optionalParameterInDestructuringWithInitializer.ts, 53, 1))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 51, 22))
+}
+
+declare function useBar2(bar: number | undefined): void;
+>useBar2 : Symbol(useBar2, Decl(optionalParameterInDestructuringWithInitializer.ts, 53, 1))
+>bar : Symbol(bar, Decl(optionalParameterInDestructuringWithInitializer.ts, 55, 25))
+
+performFoo2();
+>performFoo2 : Symbol(performFoo2, Decl(optionalParameterInDestructuringWithInitializer.ts, 49, 13))
+
diff --git a/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.types b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.types
new file mode 100644
index 00000000000..26110e71051
--- /dev/null
+++ b/tests/baselines/reference/optionalParameterInDestructuringWithInitializer.types
@@ -0,0 +1,246 @@
+=== tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts ===
+// https://github.com/Microsoft/TypeScript/issues/17080
+
+declare function f(a:number,b:number): void;
+>f : (a: number, b: number) => void
+>a : number
+>b : number
+
+function func1( {a, b}: {a: number, b?: number} = {a: 1, b: 2} ) {
+>func1 : ({ a, b }?: { a: number; b?: number | undefined; }) => void
+>a : number
+>b : number | undefined
+>a : number
+>b : number | undefined
+>{a: 1, b: 2} : { a: number; b: number; }
+>a : number
+>1 : 1
+>b : number
+>2 : 2
+
+  f(a, b)
+>f(a, b) : void
+>f : (a: number, b: number) => void
+>a : number
+>b : number | undefined
+
+  // error
+}
+
+function func2( {a, b = 3}: {a: number, b?:number} = {a: 1,b: 2} ) {
+>func2 : ({ a, b }?: { a: number; b?: number | undefined; }) => void
+>a : number
+>b : number
+>3 : 3
+>a : number
+>b : number | undefined
+>{a: 1,b: 2} : { a: number; b: number; }
+>a : number
+>1 : 1
+>b : number
+>2 : 2
+
+  f(a, b)
+>f(a, b) : void
+>f : (a: number, b: number) => void
+>a : number
+>b : number
+
+  // no error
+}
+
+function func3( {a, b}: {a: number, b?: number} = {a: 1} ) {
+>func3 : ({ a, b }?: { a: number; b?: number | undefined; }) => void
+>a : number
+>b : number | undefined
+>a : number
+>b : number | undefined
+>{a: 1} : { a: number; }
+>a : number
+>1 : 1
+
+  f(a,b)
+>f(a,b) : void
+>f : (a: number, b: number) => void
+>a : number
+>b : number | undefined
+
+  // error
+}
+
+function func4( {a: {b, c}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+>func4 : ({ a: { b, c }, d }?: { a: { b: number; c?: number | undefined; }; d: number; }) => void
+>a : any
+>b : number
+>c : number | undefined
+>d : number
+>a : { b: number; c?: number | undefined; }
+>b : number
+>c : number | undefined
+>d : number
+>{a: {b: 1,c: 2},d: 3} : { a: { b: number; c: number; }; d: number; }
+>a : { b: number; c: number; }
+>{b: 1,c: 2} : { b: number; c: number; }
+>b : number
+>1 : 1
+>c : number
+>2 : 2
+>d : number
+>3 : 3
+
+  f(b,c)
+>f(b,c) : void
+>f : (a: number, b: number) => void
+>b : number
+>c : number | undefined
+
+  // error
+}
+
+function func5({a: {b, c = 4}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+>func5 : ({ a: { b, c }, d }?: { a: { b: number; c?: number | undefined; }; d: number; }) => void
+>a : any
+>b : number
+>c : number
+>4 : 4
+>d : number
+>a : { b: number; c?: number | undefined; }
+>b : number
+>c : number | undefined
+>d : number
+>{a: {b: 1,c: 2},d: 3} : { a: { b: number; c: number; }; d: number; }
+>a : { b: number; c: number; }
+>{b: 1,c: 2} : { b: number; c: number; }
+>b : number
+>1 : 1
+>c : number
+>2 : 2
+>d : number
+>3 : 3
+
+  f(b, c)
+>f(b, c) : void
+>f : (a: number, b: number) => void
+>b : number
+>c : number
+
+  // no error
+}
+
+function func6( {a: {b, c} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1,c: 2}, d: 3} ) {
+>func6 : ({ a: { b, c }, d }?: { a: { b: number; c?: number | undefined; }; d: number; }) => void
+>a : any
+>b : number
+>c : number | undefined
+>{b: 4, c: 5} : { b: number; c: number; }
+>b : number
+>4 : 4
+>c : number
+>5 : 5
+>d : number
+>a : { b: number; c?: number | undefined; }
+>b : number
+>c : number | undefined
+>d : number
+>{a: {b: 1,c: 2}, d: 3} : { a: { b: number; c: number; }; d: number; }
+>a : { b: number; c: number; }
+>{b: 1,c: 2} : { b: number; c: number; }
+>b : number
+>1 : 1
+>c : number
+>2 : 2
+>d : number
+>3 : 3
+
+  f(b, c)
+>f(b, c) : void
+>f : (a: number, b: number) => void
+>b : number
+>c : number | undefined
+
+  // error
+}
+
+function func7( {a: {b, c = 6} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1, c: 2}, d: 3} ) {
+>func7 : ({ a: { b, c }, d }?: { a: { b: number; c?: number | undefined; }; d: number; }) => void
+>a : any
+>b : number
+>c : number
+>6 : 6
+>{b: 4, c: 5} : { b: number; c?: number; }
+>b : number
+>4 : 4
+>c : number
+>5 : 5
+>d : number
+>a : { b: number; c?: number | undefined; }
+>b : number
+>c : number | undefined
+>d : number
+>{a: {b: 1, c: 2}, d: 3} : { a: { b: number; c: number; }; d: number; }
+>a : { b: number; c: number; }
+>{b: 1, c: 2} : { b: number; c: number; }
+>b : number
+>1 : 1
+>c : number
+>2 : 2
+>d : number
+>3 : 3
+
+  f(b, c)
+>f(b, c) : void
+>f : (a: number, b: number) => void
+>b : number
+>c : number
+
+  // no error
+}
+
+interface Foo {
+>Foo : Foo
+
+  readonly bar?: number;
+>bar : number | undefined
+}
+
+function performFoo({ bar }: Foo = {}) {
+>performFoo : ({ bar }?: Foo) => void
+>bar : number | undefined
+>Foo : Foo
+>{} : {}
+
+  useBar(bar);
+>useBar(bar) : void
+>useBar : (bar: number) => void
+>bar : number | undefined
+}
+
+declare function useBar(bar: number): void;
+>useBar : (bar: number) => void
+>bar : number
+
+performFoo();
+>performFoo() : void
+>performFoo : ({ bar }?: Foo) => void
+
+function performFoo2({ bar = null }: Foo = {}) {
+>performFoo2 : ({ bar }?: Foo) => void
+>bar : number | null
+>null : null
+>Foo : Foo
+>{} : {}
+
+  useBar2(bar);
+>useBar2(bar) : void
+>useBar2 : (bar: number | undefined) => void
+>bar : number | null
+}
+
+declare function useBar2(bar: number | undefined): void;
+>useBar2 : (bar: number | undefined) => void
+>bar : number | undefined
+
+performFoo2();
+>performFoo2() : void
+>performFoo2 : ({ bar }?: Foo) => void
+
diff --git a/tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts b/tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts
new file mode 100644
index 00000000000..d3ebd99efa1
--- /dev/null
+++ b/tests/cases/compiler/optionalParameterInDestructuringWithInitializer.ts
@@ -0,0 +1,59 @@
+// @strictNullChecks: true
+// https://github.com/Microsoft/TypeScript/issues/17080
+
+declare function f(a:number,b:number): void;
+
+function func1( {a, b}: {a: number, b?: number} = {a: 1, b: 2} ) {
+  f(a, b)
+  // error
+}
+
+function func2( {a, b = 3}: {a: number, b?:number} = {a: 1,b: 2} ) {
+  f(a, b)
+  // no error
+}
+
+function func3( {a, b}: {a: number, b?: number} = {a: 1} ) {
+  f(a,b)
+  // error
+}
+
+function func4( {a: {b, c}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+  f(b,c)
+  // error
+}
+
+function func5({a: {b, c = 4}, d}: {a: {b: number,c?: number},d: number} = {a: {b: 1,c: 2},d: 3} ) {
+  f(b, c)
+  // no error
+}
+
+function func6( {a: {b, c} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1,c: 2}, d: 3} ) {
+  f(b, c)
+  // error
+}
+
+function func7( {a: {b, c = 6} = {b: 4, c: 5}, d}: {a: {b: number, c?: number}, d: number} = {a: {b: 1, c: 2}, d: 3} ) {
+  f(b, c)
+  // no error
+}
+
+interface Foo {
+  readonly bar?: number;
+}
+
+function performFoo({ bar }: Foo = {}) {
+  useBar(bar);
+}
+
+declare function useBar(bar: number): void;
+
+performFoo();
+
+function performFoo2({ bar = null }: Foo = {}) {
+  useBar2(bar);
+}
+
+declare function useBar2(bar: number | undefined): void;
+
+performFoo2();