diff --git a/reactos/subsystems/win32/win32k/eng/alphablend.c b/reactos/subsystems/win32/win32k/eng/alphablend.c
index 7ccab538e12..30ba88fd386 100644
--- a/reactos/subsystems/win32/win32k/eng/alphablend.c
+++ b/reactos/subsystems/win32/win32k/eng/alphablend.c
@@ -54,7 +54,6 @@ EngAlphaBlend(IN SURFOBJ *psoDest,
            BlendObj->BlendFunction.BlendFlags, BlendObj->BlendFunction.SourceConstantAlpha,
            BlendObj->BlendFunction.AlphaFormat);
 
-
     /* Validate output */
     OutputRect = *DestRect;
     if (OutputRect.right < OutputRect.left)
@@ -68,14 +67,12 @@ EngAlphaBlend(IN SURFOBJ *psoDest,
         OutputRect.right = DestRect->left;
     }
 
-
     /* Validate input */
-
-    /* FIXME when WindowOrg.x or .y are negitve this check are not vaild, 
-     * we need convert the inputRect to the windows org and do it right */
     InputRect = *SourceRect;
     if ( (InputRect.top < 0) || (InputRect.bottom < 0) ||
-         (InputRect.left < 0) || (InputRect.right < 0) )
+         (InputRect.left < 0) || (InputRect.right < 0) ||
+         InputRect.right > psoSource->sizlBitmap.cx || 
+         InputRect.bottom > psoSource->sizlBitmap.cy )
     {
         SetLastWin32Error(ERROR_INVALID_PARAMETER);
         return FALSE;
diff --git a/reactos/subsystems/win32/win32k/objects/bitblt.c b/reactos/subsystems/win32/win32k/objects/bitblt.c
index fe5d994efa0..29159a35d6e 100644
--- a/reactos/subsystems/win32/win32k/objects/bitblt.c
+++ b/reactos/subsystems/win32/win32k/objects/bitblt.c
@@ -49,6 +49,12 @@ NtGdiAlphaBlend(
     BLENDOBJ BlendObj;
     BlendObj.BlendFunction = BlendFunc;
 
+    if (WidthDest < 0 || HeightDest < 0 || WidthSrc < 0 || HeightSrc < 0)
+    {
+        SetLastWin32Error(ERROR_INVALID_PARAMETER);
+        return FALSE;
+    }
+
     DCDest = DC_LockDc(hDCDest);
     if (NULL == DCDest)
     {