diff --git a/test/mock/test-mock.cpp b/test/mock/test-mock.cpp
index 2707ff6..deb8fa4 100644
--- a/test/mock/test-mock.cpp
+++ b/test/mock/test-mock.cpp
@@ -22,6 +22,7 @@
 
 #include <string>
 #include <functional>
+#include <system_error>
 
 struct continuable_base {
   template <typename T> continuable_base& then(T&&) { return *this; }