diff --git a/dlls/winex11.drv/dib.c b/dlls/winex11.drv/dib.c
index cec20587533..82cacab9e9b 100644
--- a/dlls/winex11.drv/dib.c
+++ b/dlls/winex11.drv/dib.c
@@ -4608,6 +4608,7 @@ HBITMAP X11DRV_CreateDIBSection( X11DRV_PDEVICE *physDev, HBITMAP hbitmap,
 
       /* install fault handler */
     InitializeCriticalSection( &physBitmap->lock );
+    physBitmap->lock.DebugInfo->Spare[0] = (DWORD_PTR)(__FILE__ ": X_PHYSBITMAP.lock");
 
     physBitmap->base   = dib.dsBm.bmBits;
     physBitmap->size   = dib.dsBmih.biSizeImage;
@@ -4663,6 +4664,7 @@ void X11DRV_DIB_DeleteDIBSection(X_PHYSBITMAP *physBitmap, DIBSECTION *dib)
   }
 
   HeapFree(GetProcessHeap(), 0, physBitmap->colorMap);
+  physBitmap->lock.DebugInfo->Spare[0] = 0;
   DeleteCriticalSection(&physBitmap->lock);
 }