diff --git a/internal/ceres/split.cc b/internal/ceres/split.cc
index 4fa1bd4..3edbc28 100644
--- a/internal/ceres/split.cc
+++ b/internal/ceres/split.cc
@@ -28,6 +28,8 @@
 //
 // Author: keir@google.com (Keir Mierle)
 
+#include "ceres/split.h"
+
 #include <string>
 #include <vector>
 #include <iterator>