diff --git a/test_double_process.c b/test_double_process.c
index 0f4fbb8..2d4a6b0 100644
--- a/test_double_process.c
+++ b/test_double_process.c
@@ -3,6 +3,7 @@
 #include "engine.h"
 #include <stdio.h>
 #include <assert.h>
+#include <string.h>
 
 void test_command_processed_only_once(void) {
     printf("Test: Command processed only once...\n");