diff --git a/packages/babel-generator/src/generators/typescript.ts b/packages/babel-generator/src/generators/typescript.ts
index 34bfc5b914e3..cbb716f6ac4f 100644
--- a/packages/babel-generator/src/generators/typescript.ts
+++ b/packages/babel-generator/src/generators/typescript.ts
@@ -414,7 +414,7 @@ export function TSIndexedAccessType(
 }
 
 export function TSMappedType(this: Printer, node: t.TSMappedType) {
-  const { nameType, optional, readonly, typeParameter } = node;
+  const { nameType, optional, readonly, typeParameter, typeAnnotation } = node;
   this.token("{");
   this.space();
   if (readonly) {
@@ -443,13 +443,15 @@ export function TSMappedType(this: Printer, node: t.TSMappedType) {
 
   this.token("]");
 
-  if (optional) {
-    tokenIfPlusMinus(this, optional);
-    this.token("?");
+  if (typeAnnotation) {
+    if (optional) {
+      tokenIfPlusMinus(this, optional);
+      this.token("?");
+    }
+    this.token(":");
+    this.space();
+    this.print(typeAnnotation, node);
   }
-  this.token(":");
-  this.space();
-  this.print(node.typeAnnotation, node);
   this.space();
   this.token("}");
 }
diff --git a/packages/babel-generator/test/fixtures/typescript/mapped-type/input.ts b/packages/babel-generator/test/fixtures/typescript/mapped-type/input.ts
new file mode 100644
index 000000000000..9c446e4ab103
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/typescript/mapped-type/input.ts
@@ -0,0 +1 @@
+type Bar = { [key in Foo] };
diff --git a/packages/babel-generator/test/fixtures/typescript/mapped-type/output.js b/packages/babel-generator/test/fixtures/typescript/mapped-type/output.js
new file mode 100644
index 000000000000..ebccaaab98fc
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/typescript/mapped-type/output.js
@@ -0,0 +1 @@
+type Bar = { [key in Foo] };
\ No newline at end of file