@@ -615,15 +615,20 @@
 
 		i = 0;
 		while ((key = [keyEnumerator nextObject]) != nil &&
 		    (object = [objectEnumerator nextObject]) != nil) {
 			void *pool2 = objc_autoreleasePoolPush();
+			int identifierOptions =
+			    options | OF_JSON_REPRESENTATION_IDENTIFIER;
+
+			if (![key isKindOfClass: [OFString class]])
+				@throw [OFInvalidArgumentException exception];
 
 			[JSON appendString: indentation];
 			[JSON appendString: @"\t"];
 			[JSON appendString: [key
-			    OF_JSONRepresentationWithOptions: options
+			    OF_JSONRepresentationWithOptions: identifierOptions
 						       depth: depth + 1]];
 			[JSON appendString: @": "];
 			[JSON appendString: [object
 			    OF_JSONRepresentationWithOptions: options
 						       depth: depth + 1]];
@@ -640,13 +645,18 @@
 	} else {
 		i = 0;
 		while ((key = [keyEnumerator nextObject]) != nil &&
 		    (object = [objectEnumerator nextObject]) != nil) {
 			void *pool2 = objc_autoreleasePoolPush();
+			int identifierOptions =
+			    options | OF_JSON_REPRESENTATION_IDENTIFIER;
+
+			if (![key isKindOfClass: [OFString class]])
+				@throw [OFInvalidArgumentException exception];
 
 			[JSON appendString: [key
-			    OF_JSONRepresentationWithOptions: options
+			    OF_JSONRepresentationWithOptions: identifierOptions
 						       depth: depth + 1]];
 			[JSON appendString: @":"];
 			[JSON appendString: [object
 			    OF_JSONRepresentationWithOptions: options
 						       depth: depth + 1]];