diff --git a/dlls/user32/class.c b/dlls/user32/class.c
index 61edcc6ecf2..9817735aa25 100644
--- a/dlls/user32/class.c
+++ b/dlls/user32/class.c
@@ -673,7 +673,8 @@ static ULONG_PTR CLASS_GetClassLong( HWND hwnd, INT offset, UINT size,
                 case GCLP_HICONSM:
                 case GCLP_WNDPROC:
                 case GCLP_MENUNAME:
-                    FIXME( "offset %d not supported on other process window %p\n", offset, hwnd );
+                    FIXME( "offset %d (%s) not supported on other process window %p\n",
+			   offset, SPY_GetClassLongOffsetName(offset), hwnd );
                     SetLastError( ERROR_INVALID_HANDLE );
                     break;
                 case GCL_STYLE:
diff --git a/dlls/user32/spy.c b/dlls/user32/spy.c
index 451b0b25979..164101ef328 100644
--- a/dlls/user32/spy.c
+++ b/dlls/user32/spy.c
@@ -44,6 +44,24 @@ WINE_DEFAULT_DEBUG_CHANNEL(message);
 
 #define DEBUG_SPY 0
 
+static const char * const ClassLongOffsetNames[] =
+{
+    "GCLP_MENUNAME",      /*  -8 */
+    "GCLP_HBRBACKGROUND", /* -10 */
+    "GCLP_HCURSOR",       /* -12 */
+    "GCLP_HICON",         /* -14 */
+    "GCLP_HMODULE",       /* -16 */
+    "GCL_CBWNDEXTRA",     /* -18 */
+    "GCL_CBCLSEXTRA",     /* -20 */
+    "?",
+    "GCLP_WNDPROC",       /* -24 */
+    "GCL_STYLE",          /* -26 */
+    "?",
+    "?",
+    "GCW_ATOM",           /* -32 */
+    "GCLP_HICONSM",       /* -34 */
+};
+
 static const char * const MessageTypeNames[SPY_MAX_MSGNUM + 1] =
 {
     "WM_NULL",                  /* 0x00 */
@@ -2025,6 +2043,23 @@ static const USER_MSG *SPY_Bsearch_Msg( const USER_MSG *first, const USER_MSG *l
     return NULL;
 }
 
+/***********************************************************************
+ *           SPY_GetClassLongOffsetName
+ *
+ * Gets the name of a class long offset.
+ */
+const char *SPY_GetClassLongOffsetName( INT offset )
+{
+    INT index;
+    if (offset < 0 && offset % 2 == 0 && ((index = -(offset + 8) / 2) <
+	sizeof(ClassLongOffsetNames) / sizeof(*ClassLongOffsetNames)))
+    {
+        return ClassLongOffsetNames[index];
+    }
+
+    return "?";
+}
+
 /***********************************************************************
  *           SPY_GetClassName
  *
diff --git a/dlls/user32/user_private.h b/dlls/user32/user_private.h
index ae27884db84..f939e4e59e8 100644
--- a/dlls/user32/user_private.h
+++ b/dlls/user32/user_private.h
@@ -239,6 +239,7 @@ extern BOOL USER_SetWindowPos( WINDOWPOS * winpos );
 #define SPY_RESULT_DEFWND16       0x0004
 #define SPY_RESULT_DEFWND         0x0005
 
+extern const char *SPY_GetClassLongOffsetName( INT offset );
 extern const char *SPY_GetMsgName( UINT msg, HWND hWnd );
 extern const char *SPY_GetVKeyName(WPARAM wParam);
 extern void SPY_EnterMessage( INT iFlag, HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );