diff --git a/src/runtime/c/pgf/db.cxx b/src/runtime/c/pgf/db.cxx
index c4eb5a113..7167902ee 100644
--- a/src/runtime/c/pgf/db.cxx
+++ b/src/runtime/c/pgf/db.cxx
@@ -702,6 +702,7 @@ void PgfDB::init_state(size_t size)
             throw pgf_systemerror(code);
         }
     }
+    memset(&ms->rwlock, 0, sizeof(ms->rwlock)); // Apparently this is needed for MacOS
     if ((code = pthread_rwlock_init(&ms->rwlock, &attr)) != 0) {
         pthread_rwlockattr_destroy(&attr);
         throw pgf_systemerror(code);