diff --git a/lib/kwinglutils.cpp b/lib/kwinglutils.cpp
index a2395b1e6d..7c9aff5803 100644
--- a/lib/kwinglutils.cpp
+++ b/lib/kwinglutils.cpp
@@ -278,7 +278,7 @@ void renderRoundBox( const QRect& area, float roundness, GLTexture* texture )
 
     glPushMatrix();
 
-    QVector<float> verts, texcoords;
+    QVector<float> verts(80), texcoords(80);
     // center
     addQuadVertices(verts, area.left() + roundness, area.top() + roundness, area.right() - roundness, area.bottom() - roundness);
     addQuadVertices(texcoords, 0.5, 0.5, 0.5, 0.5);