diff --git a/lib/_tsc.js b/lib/_tsc.js
index ffb38a01be4fa..d1ea13710bd93 100644
--- a/lib/_tsc.js
+++ b/lib/_tsc.js
@@ -50327,7 +50327,7 @@ function createTypeChecker(host) {
           return true;
         }
         if (requiresAddingUndefined && annotationType) {
-          annotationType = getOptionalType(annotationType, !isParameter(node));
+          annotationType = addOptionality(annotationType, !isParameter(node));
         }
         return !!annotationType && typeNodeIsEquivalentToType(node, type, annotationType) && existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, type);
       }
diff --git a/lib/typescript.js b/lib/typescript.js
index 23672a730afdc..fa7c62f9a01aa 100644
--- a/lib/typescript.js
+++ b/lib/typescript.js
@@ -54930,7 +54930,7 @@ function createTypeChecker(host) {
           return true;
         }
         if (requiresAddingUndefined && annotationType) {
-          annotationType = getOptionalType(annotationType, !isParameter(node));
+          annotationType = addOptionality(annotationType, !isParameter(node));
         }
         return !!annotationType && typeNodeIsEquivalentToType(node, type, annotationType) && existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, type);
       }