diff --git a/testing_utilities/check_well_formedness_test.cpp b/testing_utilities/check_well_formedness_test.cpp
index f06c9dc24e..b924c6903d 100644
--- a/testing_utilities/check_well_formedness_test.cpp
+++ b/testing_utilities/check_well_formedness_test.cpp
@@ -1,6 +1,7 @@
 #include "testing_utilities/check_well_formedness.hpp"
 
 #include <string>
+#include <utility>
 
 PRINCIPIA_CHECK_ILL_FORMED(s + 3, WITH<std::string> s);
 PRINCIPIA_CHECK_ILL_FORMED(s + "3", WITH<std::pair<double, double>> s);