diff --git a/src/lib/es2015.iterable.d.ts b/src/lib/es2015.iterable.d.ts
index 20b6920e0d6..f1fb454f980 100644
--- a/src/lib/es2015.iterable.d.ts
+++ b/src/lib/es2015.iterable.d.ts
@@ -137,7 +137,8 @@ interface ReadonlyMap<K, V> {
 }
 
 interface MapConstructor {
-    new <K, V>(iterable: Iterable<readonly [K, V]>): Map<K, V>;
+    new(): Map<any, any>;
+    new <K, V>(iterable?: Iterable<readonly [K, V]> | null): Map<K, V>;
 }
 
 interface WeakMap<K extends object, V> { }
diff --git a/tests/baselines/reference/for-of39.errors.txt b/tests/baselines/reference/for-of39.errors.txt
index c887c20ef4b..fc45150a38c 100644
--- a/tests/baselines/reference/for-of39.errors.txt
+++ b/tests/baselines/reference/for-of39.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/for-ofStatements/for-of39.ts(1,11): error TS2769: No overload matches this call.
-  Overload 1 of 3, '(iterable: Iterable<readonly [string, boolean]>): Map<string, boolean>', gave the following error.
+  Overload 1 of 4, '(iterable?: Iterable<readonly [string, boolean]>): Map<string, boolean>', gave the following error.
     Argument of type '([string, number] | [string, true])[]' is not assignable to parameter of type 'Iterable<readonly [string, boolean]>'.
       The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
         Type 'IteratorResult<[string, number] | [string, true], any>' is not assignable to type 'IteratorResult<readonly [string, boolean], any>'.
@@ -9,7 +9,7 @@ tests/cases/conformance/es6/for-ofStatements/for-of39.ts(1,11): error TS2769: No
                 Type '[string, number]' is not assignable to type 'readonly [string, boolean]'.
                   Type at position 1 in source is not compatible with type at position 1 in target.
                     Type 'number' is not assignable to type 'boolean'.
-  Overload 2 of 3, '(entries?: readonly (readonly [string, boolean])[]): Map<string, boolean>', gave the following error.
+  Overload 2 of 4, '(entries?: readonly (readonly [string, boolean])[]): Map<string, boolean>', gave the following error.
     Type 'number' is not assignable to type 'boolean'.
 
 
@@ -17,7 +17,7 @@ tests/cases/conformance/es6/for-ofStatements/for-of39.ts(1,11): error TS2769: No
     var map = new Map([["", true], ["", 0]]);
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2769: No overload matches this call.
-!!! error TS2769:   Overload 1 of 3, '(iterable: Iterable<readonly [string, boolean]>): Map<string, boolean>', gave the following error.
+!!! error TS2769:   Overload 1 of 4, '(iterable?: Iterable<readonly [string, boolean]>): Map<string, boolean>', gave the following error.
 !!! error TS2769:     Argument of type '([string, number] | [string, true])[]' is not assignable to parameter of type 'Iterable<readonly [string, boolean]>'.
 !!! error TS2769:       The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
 !!! error TS2769:         Type 'IteratorResult<[string, number] | [string, true], any>' is not assignable to type 'IteratorResult<readonly [string, boolean], any>'.
@@ -27,7 +27,7 @@ tests/cases/conformance/es6/for-ofStatements/for-of39.ts(1,11): error TS2769: No
 !!! error TS2769:                 Type '[string, number]' is not assignable to type 'readonly [string, boolean]'.
 !!! error TS2769:                   Type at position 1 in source is not compatible with type at position 1 in target.
 !!! error TS2769:                     Type 'number' is not assignable to type 'boolean'.
-!!! error TS2769:   Overload 2 of 3, '(entries?: readonly (readonly [string, boolean])[]): Map<string, boolean>', gave the following error.
+!!! error TS2769:   Overload 2 of 4, '(entries?: readonly (readonly [string, boolean])[]): Map<string, boolean>', gave the following error.
 !!! error TS2769:     Type 'number' is not assignable to type 'boolean'.
     for (var [k, v] of map) {
         k;
diff --git a/tests/baselines/reference/iterableArrayPattern28.errors.txt b/tests/baselines/reference/iterableArrayPattern28.errors.txt
index b47f3b2c993..b56659f48b9 100644
--- a/tests/baselines/reference/iterableArrayPattern28.errors.txt
+++ b/tests/baselines/reference/iterableArrayPattern28.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,24): error TS2769: No overload matches this call.
-  Overload 1 of 3, '(iterable: Iterable<readonly [string, number]>): Map<string, number>', gave the following error.
+  Overload 1 of 4, '(iterable?: Iterable<readonly [string, number]>): Map<string, number>', gave the following error.
     Argument of type '([string, number] | [string, boolean])[]' is not assignable to parameter of type 'Iterable<readonly [string, number]>'.
       The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
         Type 'IteratorResult<[string, number] | [string, boolean], any>' is not assignable to type 'IteratorResult<readonly [string, number], any>'.
@@ -9,7 +9,7 @@ tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,24): error
                 Type '[string, boolean]' is not assignable to type 'readonly [string, number]'.
                   Type at position 1 in source is not compatible with type at position 1 in target.
                     Type 'boolean' is not assignable to type 'number'.
-  Overload 2 of 3, '(entries?: readonly (readonly [string, number])[]): Map<string, number>', gave the following error.
+  Overload 2 of 4, '(entries?: readonly (readonly [string, number])[]): Map<string, number>', gave the following error.
     Type 'boolean' is not assignable to type 'number'.
 
 
@@ -18,7 +18,7 @@ tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,24): error
     takeFirstTwoEntries(...new Map([["", 0], ["hello", true]]));
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2769: No overload matches this call.
-!!! error TS2769:   Overload 1 of 3, '(iterable: Iterable<readonly [string, number]>): Map<string, number>', gave the following error.
+!!! error TS2769:   Overload 1 of 4, '(iterable?: Iterable<readonly [string, number]>): Map<string, number>', gave the following error.
 !!! error TS2769:     Argument of type '([string, number] | [string, boolean])[]' is not assignable to parameter of type 'Iterable<readonly [string, number]>'.
 !!! error TS2769:       The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
 !!! error TS2769:         Type 'IteratorResult<[string, number] | [string, boolean], any>' is not assignable to type 'IteratorResult<readonly [string, number], any>'.
@@ -28,5 +28,5 @@ tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,24): error
 !!! error TS2769:                 Type '[string, boolean]' is not assignable to type 'readonly [string, number]'.
 !!! error TS2769:                   Type at position 1 in source is not compatible with type at position 1 in target.
 !!! error TS2769:                     Type 'boolean' is not assignable to type 'number'.
-!!! error TS2769:   Overload 2 of 3, '(entries?: readonly (readonly [string, number])[]): Map<string, number>', gave the following error.
+!!! error TS2769:   Overload 2 of 4, '(entries?: readonly (readonly [string, number])[]): Map<string, number>', gave the following error.
 !!! error TS2769:     Type 'boolean' is not assignable to type 'number'.
\ No newline at end of file
diff --git a/tests/baselines/reference/mapConstructor.js b/tests/baselines/reference/mapConstructor.js
new file mode 100644
index 00000000000..bb0b9e0697c
--- /dev/null
+++ b/tests/baselines/reference/mapConstructor.js
@@ -0,0 +1,16 @@
+//// [mapConstructor.ts]
+new Map();
+
+const potentiallyUndefinedIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | undefined;
+new Map(potentiallyUndefinedIterable);
+
+const potentiallyNullIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | null;
+new Map(potentiallyNullIterable);
+
+//// [mapConstructor.js]
+"use strict";
+new Map();
+const potentiallyUndefinedIterable = [['1', 1], ['2', 2]];
+new Map(potentiallyUndefinedIterable);
+const potentiallyNullIterable = [['1', 1], ['2', 2]];
+new Map(potentiallyNullIterable);
diff --git a/tests/baselines/reference/mapConstructor.symbols b/tests/baselines/reference/mapConstructor.symbols
new file mode 100644
index 00000000000..a37ecb3b56c
--- /dev/null
+++ b/tests/baselines/reference/mapConstructor.symbols
@@ -0,0 +1,20 @@
+=== tests/cases/compiler/mapConstructor.ts ===
+new Map();
+>Map : Symbol(Map, Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+const potentiallyUndefinedIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | undefined;
+>potentiallyUndefinedIterable : Symbol(potentiallyUndefinedIterable, Decl(mapConstructor.ts, 2, 5))
+>Iterable : Symbol(Iterable, Decl(lib.es2015.iterable.d.ts, --, --))
+
+new Map(potentiallyUndefinedIterable);
+>Map : Symbol(Map, Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>potentiallyUndefinedIterable : Symbol(potentiallyUndefinedIterable, Decl(mapConstructor.ts, 2, 5))
+
+const potentiallyNullIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | null;
+>potentiallyNullIterable : Symbol(potentiallyNullIterable, Decl(mapConstructor.ts, 5, 5))
+>Iterable : Symbol(Iterable, Decl(lib.es2015.iterable.d.ts, --, --))
+
+new Map(potentiallyNullIterable);
+>Map : Symbol(Map, Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>potentiallyNullIterable : Symbol(potentiallyNullIterable, Decl(mapConstructor.ts, 5, 5))
+
diff --git a/tests/baselines/reference/mapConstructor.types b/tests/baselines/reference/mapConstructor.types
new file mode 100644
index 00000000000..6531580d8da
--- /dev/null
+++ b/tests/baselines/reference/mapConstructor.types
@@ -0,0 +1,38 @@
+=== tests/cases/compiler/mapConstructor.ts ===
+new Map();
+>new Map() : Map<any, any>
+>Map : MapConstructor
+
+const potentiallyUndefinedIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | undefined;
+>potentiallyUndefinedIterable : Iterable<[string, number]> | undefined
+>[['1', 1], ['2', 2]] as Iterable<[string, number]> | undefined : Iterable<[string, number]> | undefined
+>[['1', 1], ['2', 2]] : [string, number][]
+>['1', 1] : [string, number]
+>'1' : "1"
+>1 : 1
+>['2', 2] : [string, number]
+>'2' : "2"
+>2 : 2
+
+new Map(potentiallyUndefinedIterable);
+>new Map(potentiallyUndefinedIterable) : Map<string, number>
+>Map : MapConstructor
+>potentiallyUndefinedIterable : Iterable<[string, number]> | undefined
+
+const potentiallyNullIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | null;
+>potentiallyNullIterable : Iterable<[string, number]> | null
+>[['1', 1], ['2', 2]] as Iterable<[string, number]> | null : Iterable<[string, number]> | null
+>[['1', 1], ['2', 2]] : [string, number][]
+>['1', 1] : [string, number]
+>'1' : "1"
+>1 : 1
+>['2', 2] : [string, number]
+>'2' : "2"
+>2 : 2
+>null : null
+
+new Map(potentiallyNullIterable);
+>new Map(potentiallyNullIterable) : Map<string, number>
+>Map : MapConstructor
+>potentiallyNullIterable : Iterable<[string, number]> | null
+
diff --git a/tests/baselines/reference/newMap.types b/tests/baselines/reference/newMap.types
index c00ff104407..ee684b26e00 100644
--- a/tests/baselines/reference/newMap.types
+++ b/tests/baselines/reference/newMap.types
@@ -1,5 +1,5 @@
 === tests/cases/compiler/newMap.ts ===
 new Map<string>();
->new Map<string>() : Map<string, unknown>
+>new Map<string>() : Map<any, any>
 >Map : MapConstructor
 
diff --git a/tests/cases/compiler/mapConstructor.ts b/tests/cases/compiler/mapConstructor.ts
new file mode 100644
index 00000000000..7d1124579e6
--- /dev/null
+++ b/tests/cases/compiler/mapConstructor.ts
@@ -0,0 +1,10 @@
+// @strict: true
+// @target: es2015
+
+new Map();
+
+const potentiallyUndefinedIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | undefined;
+new Map(potentiallyUndefinedIterable);
+
+const potentiallyNullIterable = [['1', 1], ['2', 2]] as Iterable<[string, number]> | null;
+new Map(potentiallyNullIterable);
\ No newline at end of file