diff --git a/dll/win32/rpcrt4/rpcrt4_main.c b/dll/win32/rpcrt4/rpcrt4_main.c
index 67a3dbe595f..7cc8d0b06b2 100644
--- a/dll/win32/rpcrt4/rpcrt4_main.c
+++ b/dll/win32/rpcrt4/rpcrt4_main.c
@@ -158,6 +158,7 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
 RPC_STATUS WINAPI RpcStringFreeA(RPC_CSTR* String)
 {
   HeapFree( GetProcessHeap(), 0, *String);
+  if (String) *String = NULL;
 
   return RPC_S_OK;
 }
@@ -174,6 +175,7 @@ RPC_STATUS WINAPI RpcStringFreeA(RPC_CSTR* String)
 RPC_STATUS WINAPI RpcStringFreeW(RPC_WSTR* String)
 {
   HeapFree( GetProcessHeap(), 0, *String);
+  if (String) *String = NULL;
 
   return RPC_S_OK;
 }
diff --git a/modules/rostests/winetests/rpcrt4/rpc.c b/modules/rostests/winetests/rpcrt4/rpc.c
index d3a3aee6c8c..dcf7a2d9608 100644
--- a/modules/rostests/winetests/rpcrt4/rpc.c
+++ b/modules/rostests/winetests/rpcrt4/rpc.c
@@ -854,6 +854,22 @@ static void test_RpcBindingFree(void)
        status);
 }
 
+static void test_RpcStringFree(void)
+{
+    RPC_WSTR string = NULL;
+
+    string = HeapAlloc(GetProcessHeap(), 0, 10*sizeof(WCHAR));
+    if (string == NULL)
+    {
+        skip("Failed to allocate a string!\n");
+        return;
+    }
+
+    RpcStringFreeW(&string);
+
+    ok(string == NULL, "String is %p expected NULL!\n", string);
+}
+
 static void test_RpcServerInqDefaultPrincName(void)
 {
     RPC_STATUS ret;
@@ -1204,6 +1220,7 @@ START_TEST( rpc )
     test_UuidCreate();
     test_UuidCreateSequential();
     test_RpcBindingFree();
+    test_RpcStringFree();
     test_RpcServerInqDefaultPrincName();
     test_RpcServerRegisterAuthInfo();