diff --git a/dtool/dtool_config.h.in b/dtool/dtool_config.h.in
index 186bea89b2..7d0114a3fc 100644
--- a/dtool/dtool_config.h.in
+++ b/dtool/dtool_config.h.in
@@ -116,7 +116,7 @@
 
 /* Define if we have OpenGL installed and want to build for GL.  */
 #cmakedefine HAVE_GL
-#if HAVE_GL
+#ifdef HAVE_GL
 #cmakedefine MIN_GL_VERSION_MAJOR
 #cmakedefine MIN_GL_VERSION_MINOR
 #endif