diff --git a/internal/ceres/test_util.cc b/internal/ceres/test_util.cc
index 8a1def7..a3f67bd 100644
--- a/internal/ceres/test_util.cc
+++ b/internal/ceres/test_util.cc
@@ -33,6 +33,7 @@
 #include <cmath>
 #include "ceres/file.h"
 #include "ceres/stringprintf.h"
+#include "gflags/gflags.h"
 #include "glog/logging.h"
 #include "gtest/gtest.h"