diff --git a/python/mrc/tests/utils.cpp b/python/mrc/tests/utils.cpp
index fd95679ce..1223b7384 100644
--- a/python/mrc/tests/utils.cpp
+++ b/python/mrc/tests/utils.cpp
@@ -22,6 +22,7 @@
 
 #include <glog/logging.h>
 #include <pybind11/cast.h>
+#include <pybind11/gil.h>  // for gil_scoped_acquire
 #include <pybind11/pybind11.h>
 #include <pybind11/pytypes.h>