diff --git a/xs/sources/xsJSON.c b/xs/sources/xsJSON.c
index c49da7e71..a60cd0e7f 100644
--- a/xs/sources/xsJSON.c
+++ b/xs/sources/xsJSON.c
@@ -816,6 +816,7 @@ void fxStringifyJSONProperty(txMachine* the, txJSONStringifier* theStringifier,
 		anInstance = C_NULL;
 	if (theStringifier->replacer) {
 		mxPushSlot(aKey);
+		fxToString(the, the->stack);
 		mxPushSlot(aValue);
 		/* COUNT */
 		mxPushInteger(2);