diff --git a/dlls/user32/listbox.c b/dlls/user32/listbox.c
index 826ce01cc40..9bf9f9023c6 100644
--- a/dlls/user32/listbox.c
+++ b/dlls/user32/listbox.c
@@ -156,6 +156,11 @@ static ULONG_PTR get_item_data( const LB_DESCR *descr, UINT index )
     return (descr->style & LBS_NODATA) ? 0 : descr->items[index].data;
 }
 
+static void set_item_data( LB_DESCR *descr, UINT index, ULONG_PTR data )
+{
+    if (!(descr->style & LBS_NODATA)) descr->items[index].data = data;
+}
+
 static WCHAR *get_item_string( const LB_DESCR *descr, UINT index )
 {
     return HAS_STRINGS(descr) ? descr->items[index].str : NULL;
@@ -2743,7 +2748,7 @@ LRESULT ListBoxWndProc_common( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam
             SetLastError(ERROR_INVALID_INDEX);
             return LB_ERR;
         }
-        if (!(descr->style & LBS_NODATA)) descr->items[wParam].data = lParam;
+        set_item_data(descr, wParam, lParam);
         /* undocumented: returns TRUE, not LB_OKAY (0) */
         return TRUE;