diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 818b24ca8fd..8f1c05adabe 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -232,8 +232,8 @@ namespace ts {
 
     // Add an extra underscore to identifiers that start with two underscores to avoid issues with magic names like '__proto__'
     export function escapeIdentifier(identifier: string): string {
-        const prefixWithUnderscore = identifier.length > 2 && identifier.charCodeAt(0) === CharacterCodes._ && identifier.charCodeAt(1) === CharacterCodes._;
-        return prefixWithUnderscore ? "_" + identifier : identifier;
+        const prefixedWithUnderscores = identifier.length >= 3 && identifier.charCodeAt(0) === CharacterCodes._ && identifier.charCodeAt(1) === CharacterCodes._;
+        return prefixedWithUnderscores ? "_" + identifier : identifier;
     }
 
     // Remove extra underscore from escaped identifier