diff --git a/lib/kwineffects.cpp b/lib/kwineffects.cpp
index 96973d2cb1..9e16e28058 100644
--- a/lib/kwineffects.cpp
+++ b/lib/kwineffects.cpp
@@ -597,6 +597,11 @@ WindowQuadList WindowQuadList::splitAtX( double x ) const
             ret.append( quad );
             continue;
             }
+        if( quad.left() == quad.right() ) // quad has no size
+            {
+            ret.append( quad );
+            continue;
+            }
         ret.append( quad.makeSubQuad( quad.left(), quad.top(), x, quad.bottom()));
         ret.append( quad.makeSubQuad( x, quad.top(), quad.right(), quad.bottom()));
         }
@@ -628,6 +633,11 @@ WindowQuadList WindowQuadList::splitAtY( double y ) const
             ret.append( quad );
             continue;
             }
+        if( quad.top() == quad.bottom() ) // quad has no size
+            {
+            ret.append( quad );
+            continue;
+            }
         ret.append( quad.makeSubQuad( quad.left(), quad.top(), quad.right(), y ));
         ret.append( quad.makeSubQuad( quad.left(), y, quad.right(), quad.bottom()));
         }