diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d64d1e5da3b..ff3ec78a931 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -24122,7 +24122,7 @@ namespace ts {
         }
 
         function isGenericTypeWithUnionConstraint(type: Type) {
-            return !!(type.flags & TypeFlags.Instantiable && getBaseConstraintOrType(type).flags & TypeFlags.Union);
+            return !!(type.flags & TypeFlags.Instantiable && getBaseConstraintOrType(type).flags & (TypeFlags.Nullable | TypeFlags.Union));
         }
 
         function containsGenericType(type: Type): boolean {