diff --git a/src/kernel/syscalls/endpoint.cpp b/src/kernel/syscalls/endpoint.cpp
index 1821829..0dd0787 100644
--- a/src/kernel/syscalls/endpoint.cpp
+++ b/src/kernel/syscalls/endpoint.cpp
@@ -29,7 +29,7 @@ endpoint_send(j6_handle_t handle, uint64_t tag, const void * data, size_t data_l
 j6_status_t
 endpoint_receive(j6_handle_t handle, uint64_t * tag, void * data, size_t * data_len)
 {
-    if (!tag || !data_len || !data)
+    if (!tag || !data_len || (*data_len && !data))
         return j6_err_invalid_arg;
 
     endpoint *e = get_handle<endpoint>(handle);
diff --git a/src/user/testapp/main.cpp b/src/user/testapp/main.cpp
index 4aa523f..4cfd24b 100644
--- a/src/user/testapp/main.cpp
+++ b/src/user/testapp/main.cpp
@@ -134,7 +134,7 @@ main(int argc, const char **argv)
 
     size_t len = 0;
     while (true) {
-        result = j6_endpoint_receive(endp, &tag, &len, nullptr);
+        result = j6_endpoint_receive(endp, &tag, nullptr, &len);
         if (result != j6_status_ok)
             return result;