diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index e2f832c9580..2cfd0ca94c0 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1207,7 +1207,7 @@ namespace ts {
         }
 
         // Resolves a qualified name and any involved aliases
-        function resolveEntityName(name: EntityName | Expression, meaning: SymbolFlags, ignoreErrors = false, dontResolveAlias = false): Symbol {
+        function resolveEntityName(name: EntityName | Expression, meaning: SymbolFlags, ignoreErrors?: boolean, dontResolveAlias?: boolean): Symbol {
             if (nodeIsMissing(name)) {
                 return undefined;
             }