diff --git a/tests/unit/plugins/relay/api/test-relay-api-protocol.cpp b/tests/unit/plugins/relay/api/test-relay-api-protocol.cpp
index 0b41472a1..51ad18947 100644
--- a/tests/unit/plugins/relay/api/test-relay-api-protocol.cpp
+++ b/tests/unit/plugins/relay/api/test-relay-api-protocol.cpp
@@ -26,6 +26,7 @@
 extern "C"
 {
 #include <unistd.h>
+#include <string.h>
 #include <cjson/cJSON.h>
 #include "src/core/core-config-file.h"
 #include "src/core/core-string.h"