diff --git a/tests/unit/core/test-core-hdata.cpp b/tests/unit/core/test-core-hdata.cpp
index 008a5c4f0..815434dd4 100644
--- a/tests/unit/core/test-core-hdata.cpp
+++ b/tests/unit/core/test-core-hdata.cpp
@@ -23,6 +23,7 @@
 
 extern "C"
 {
+#include <string.h>
 #include "src/core/wee-hdata.h"
 #include "src/core/wee-config.h"
 #include "src/core/wee-hashtable.h"