--- a/js/src/frontend/BinSource.cpp
+++ b/js/src/frontend/BinSource.cpp
@@ -2289,16 +2289,36 @@ ASTReader::parseSwitchCase(SimpleTokenRe
     Unused << test.release();
     Unused << statements.release();
 
     out = Move(result);
     return true;
 }
 
 bool
+ASTReader::readString(SimpleTokenReader* reader, MutableHandle<PropertyName*> out) {
+    if (out) {
+        return this->raiseError();
+    }
+
+    RootedAtom atom(cx);
+
+    if (!this->readString(reader, &atom)) {
+        return false;
+    }
+
+    if (!atom) {
+        out.set(nullptr);
+    } else {
+        out.set(atom->asPropertyName());
+    }
+    return true;
+}
+
+bool
 ASTReader::readString(SimpleTokenReader* reader, Maybe<std::string>& out) {
     if (out) {
         return this->raiseError();
     }
 
     if (!reader->readMaybeString(&out)) {
         return false;
     }