diff --git a/testing/fx_string_testhelpers.cpp b/testing/fx_string_testhelpers.cpp
index 8adf382..1c057e6 100644
--- a/testing/fx_string_testhelpers.cpp
+++ b/testing/fx_string_testhelpers.cpp
@@ -7,6 +7,7 @@
 #include <iomanip>
 #include <ios>
 
+#include "core/fxcrt/cfx_datetime.h"
 #include "core/fxcrt/fx_string.h"
 #include "third_party/base/check.h"
 #include "third_party/base/span.h"