diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index f984c12fb68..acf01bac905 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -442,6 +442,8 @@ namespace ts {
                 case ModuleResolutionKind.Classic:
                     result = classicNameResolver(moduleName, containingFile, compilerOptions, host, cache);
                     break;
+                default:
+                    Debug.fail(`Unexpected moduleResolution: ${moduleResolution}`);
             }
 
             if (perFolderCache) {