diff --git a/poppler/SplashOutputDev.cc b/poppler/SplashOutputDev.cc
index d9ea990..8c69502 100644
--- a/poppler/SplashOutputDev.cc
+++ b/poppler/SplashOutputDev.cc
@@ -3802,7 +3802,7 @@
   transpGroup->ty = ty;
   transpGroup->blendingColorSpace = blendingColorSpace;
   transpGroup->isolated = isolated;
-  transpGroup->shape = (knockout) ? SplashBitmap::copy(bitmap) : NULL;
+  transpGroup->shape = (knockout && !isolated) ? SplashBitmap::copy(bitmap) : NULL;
   transpGroup->knockout = gFalse; 
   transpGroup->knockoutOpacity = 1.0;
   transpGroup->next = transpGroupStack;