diff --git a/src/z3c/json/proxy.py b/src/z3c/json/proxy.py
index 83f8769..584c77a 100644
--- a/src/z3c/json/proxy.py
+++ b/src/z3c/json/proxy.py
@@ -100,6 +100,9 @@ def __request(self, request):
         
         This will raise a ResponseError or return the JSON result dict
         """
+        # apply encoding if any
+        if self.__encoding:
+            request = request.encode(self.__encoding)
         # start the call
         try:
             response = self.__transport.request(self.__host, self.__handler,