diff --git a/src/services/inlayHints.ts b/src/services/inlayHints.ts
index f36b6e7d087..110e9718405 100644
--- a/src/services/inlayHints.ts
+++ b/src/services/inlayHints.ts
@@ -279,7 +279,7 @@ namespace ts.InlayHints {
                     continue;
                 }
 
-                addTypeHints(typeDisplayString, param.name.end);
+                addTypeHints(typeDisplayString, param.questionToken ? param.questionToken.end : param.name.end);
             }
         }
 
diff --git a/tests/cases/fourslash/inlayHintsShouldWork66.ts b/tests/cases/fourslash/inlayHintsShouldWork66.ts
new file mode 100644
index 00000000000..618348a6911
--- /dev/null
+++ b/tests/cases/fourslash/inlayHintsShouldWork66.ts
@@ -0,0 +1,23 @@
+/// <reference path="fourslash.ts" />
+
+////interface IFoo {
+////    bar(x?: boolean): void;
+////}
+////
+////const a: IFoo = {
+////    bar: function (x?/**/): void {
+////        throw new Error("Function not implemented.");
+////    }
+////}
+
+const [marker] = test.markers();
+verify.getInlayHints([
+    {
+        text: ': boolean',
+        position: marker.position,
+        kind: ts.InlayHintKind.Type,
+        whitespaceBefore: true
+    },
+], undefined, {
+    includeInlayFunctionParameterTypeHints: true
+});