diff --git a/src/gui/kernel/qsurfaceformat.cpp b/src/gui/kernel/qsurfaceformat.cpp
index 1a94ecacdc..063e68d29f 100644
--- a/src/gui/kernel/qsurfaceformat.cpp
+++ b/src/gui/kernel/qsurfaceformat.cpp
@@ -337,7 +337,7 @@ void QSurfaceFormat::setGreenBufferSize(int size)
 
 void QSurfaceFormat::setBlueBufferSize(int size)
 {
-    if (d->blueBufferSize = size) {
+    if (d->blueBufferSize != size) {
         detach();
         d->blueBufferSize = size;
     }