diff --git a/src/gen_cpp_Message.ysl2 b/src/gen_cpp_Message.ysl2
index ecefa1e..2e587de 100644
--- a/src/gen_cpp_Message.ysl2
+++ b/src/gen_cpp_Message.ysl2
@@ -12,6 +12,7 @@ tstylesheet {
 
         document("foundation_pEp_jniadapter_{$jname}.cc", "text") {
             ||
+            #include <cassert>
             #include <pEp/mime.h>
             #include <pEp/pEpLog.hh>
             #include "jniutils.hh"