diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f0cb233cb75..c77f9dd6527 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11395,7 +11395,7 @@ namespace ts {
                         // such that direct inferences to T get priority over inferences to Partial<T>, for example.
                         const inference = getInferenceInfoForType((<IndexType>constraintType).type);
                         if (inference && !inference.isFixed) {
-                            const key = (source.symbol ? getSymbolId(source.symbol) : "no symbol") + "," + getSymbolId(target.symbol);
+                            const key = (source.symbol ? getSymbolId(source.symbol) + "," : "") + getSymbolId(target.symbol);
                             if (contains(mappedTypeStack, key)) {
                                 return;
                             }