diff --git a/dtool/src/cppparser/cppManifest.cxx b/dtool/src/cppparser/cppManifest.cxx
index 0ff4ad14d3..db8122a3d6 100644
--- a/dtool/src/cppparser/cppManifest.cxx
+++ b/dtool/src/cppparser/cppManifest.cxx
@@ -13,6 +13,7 @@
 
 #include "cppManifest.h"
 #include "cppExpression.h"
+#include "cppPreprocessor.h"
 
 #include <ctype.h>