diff --git a/effects/blur/blur.cpp b/effects/blur/blur.cpp
index 1c1a92e5c7..f4e4061090 100644
--- a/effects/blur/blur.cpp
+++ b/effects/blur/blur.cpp
@@ -416,7 +416,7 @@ QRegion BlurEffect::blurRegion(const EffectWindow *w) const
         const QRegion appRegion = qvariant_cast<QRegion>(value);
         if (!appRegion.isEmpty()) {
             if (w->decorationHasAlpha() && effects->decorationSupportsBlurBehind()) {
-                region = w->shape();
+                region = w->shape() & w->rect();
                 region -= w->decorationInnerRect();
             }
             region |= appRegion.translated(w->contentsRect().topLeft()) &
@@ -424,12 +424,12 @@ QRegion BlurEffect::blurRegion(const EffectWindow *w) const
         } else {
             // An empty region means that the blur effect should be enabled
             // for the whole window.
-            region = w->shape();
+            region = w->shape() & w->rect();
         }
     } else if (w->decorationHasAlpha() && effects->decorationSupportsBlurBehind()) {
         // If the client hasn't specified a blur region, we'll only enable
         // the effect behind the decoration.
-        region = w->shape();
+        region = w->shape() & w->rect();
         region -= w->decorationInnerRect();
     }