diff --git a/compositingprefs.cpp b/compositingprefs.cpp
index a4698c6251..b0bcc51d57 100644
--- a/compositingprefs.cpp
+++ b/compositingprefs.cpp
@@ -129,7 +129,7 @@ void CompositingPrefs::detect()
     // remember and later restore active context
     GLXContext oldcontext = glXGetCurrentContext();
     GLXDrawable olddrawable = glXGetCurrentDrawable();
-    GLXDrawable oldreaddrawable;
+    GLXDrawable oldreaddrawable = None;
     if( hasglx13 )
         oldreaddrawable = glXGetCurrentReadDrawable();