diff --git a/src/compiler/declarationEmitter.ts b/src/compiler/declarationEmitter.ts
index a9b3568bfe6..43c635db2f2 100644
--- a/src/compiler/declarationEmitter.ts
+++ b/src/compiler/declarationEmitter.ts
@@ -608,7 +608,12 @@ namespace ts {
                         "?");
                 }
                 write(": ");
-                emitType(node.type);
+                if (node.type) {
+                    emitType(node.type);
+                }
+                else {
+                    write("any");
+                }
                 write(";");
                 writeLine();
                 decreaseIndent();
diff --git a/tests/baselines/reference/mappedTypeNoTypeNoCrash.errors.txt b/tests/baselines/reference/mappedTypeNoTypeNoCrash.errors.txt
new file mode 100644
index 00000000000..1e32656c699
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeNoTypeNoCrash.errors.txt
@@ -0,0 +1,16 @@
+tests/cases/compiler/mappedTypeNoTypeNoCrash.ts(1,51): error TS2304: Cannot find name 'K'.
+tests/cases/compiler/mappedTypeNoTypeNoCrash.ts(1,51): error TS4081: Exported type alias 'T0' has or is using private name 'K'.
+tests/cases/compiler/mappedTypeNoTypeNoCrash.ts(1,57): error TS2304: Cannot find name 'K'.
+tests/cases/compiler/mappedTypeNoTypeNoCrash.ts(1,57): error TS4081: Exported type alias 'T0' has or is using private name 'K'.
+
+
+==== tests/cases/compiler/mappedTypeNoTypeNoCrash.ts (4 errors) ====
+    type T0<T> = ({[K in keyof T]}) extends ({[key in K]: T[K]}) ? number : never;
+                                                      ~
+!!! error TS2304: Cannot find name 'K'.
+                                                      ~
+!!! error TS4081: Exported type alias 'T0' has or is using private name 'K'.
+                                                            ~
+!!! error TS2304: Cannot find name 'K'.
+                                                            ~
+!!! error TS4081: Exported type alias 'T0' has or is using private name 'K'.
\ No newline at end of file
diff --git a/tests/baselines/reference/mappedTypeNoTypeNoCrash.js b/tests/baselines/reference/mappedTypeNoTypeNoCrash.js
new file mode 100644
index 00000000000..ad1d9bba0bf
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeNoTypeNoCrash.js
@@ -0,0 +1,4 @@
+//// [mappedTypeNoTypeNoCrash.ts]
+type T0<T> = ({[K in keyof T]}) extends ({[key in K]: T[K]}) ? number : never;
+
+//// [mappedTypeNoTypeNoCrash.js]
diff --git a/tests/baselines/reference/mappedTypeNoTypeNoCrash.symbols b/tests/baselines/reference/mappedTypeNoTypeNoCrash.symbols
new file mode 100644
index 00000000000..7faf2d7b35f
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeNoTypeNoCrash.symbols
@@ -0,0 +1,9 @@
+=== tests/cases/compiler/mappedTypeNoTypeNoCrash.ts ===
+type T0<T> = ({[K in keyof T]}) extends ({[key in K]: T[K]}) ? number : never;
+>T0 : Symbol(T0, Decl(mappedTypeNoTypeNoCrash.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeNoTypeNoCrash.ts, 0, 8))
+>K : Symbol(K, Decl(mappedTypeNoTypeNoCrash.ts, 0, 16))
+>T : Symbol(T, Decl(mappedTypeNoTypeNoCrash.ts, 0, 8))
+>key : Symbol(key, Decl(mappedTypeNoTypeNoCrash.ts, 0, 43))
+>T : Symbol(T, Decl(mappedTypeNoTypeNoCrash.ts, 0, 8))
+
diff --git a/tests/baselines/reference/mappedTypeNoTypeNoCrash.types b/tests/baselines/reference/mappedTypeNoTypeNoCrash.types
new file mode 100644
index 00000000000..0ec1e7723f8
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeNoTypeNoCrash.types
@@ -0,0 +1,11 @@
+=== tests/cases/compiler/mappedTypeNoTypeNoCrash.ts ===
+type T0<T> = ({[K in keyof T]}) extends ({[key in K]: T[K]}) ? number : never;
+>T0 : number
+>T : T
+>K : K
+>T : T
+>key : key
+>K : No type information available!
+>T : T
+>K : No type information available!
+
diff --git a/tests/cases/compiler/mappedTypeNoTypeNoCrash.ts b/tests/cases/compiler/mappedTypeNoTypeNoCrash.ts
new file mode 100644
index 00000000000..fc9760c7a69
--- /dev/null
+++ b/tests/cases/compiler/mappedTypeNoTypeNoCrash.ts
@@ -0,0 +1,2 @@
+// @declaration: true
+type T0<T> = ({[K in keyof T]}) extends ({[key in K]: T[K]}) ? number : never;
\ No newline at end of file