diff --git a/tests/src/conc_increment.c b/tests/src/conc_increment.c
index 4b39b13..5caf762 100644
--- a/tests/src/conc_increment.c
+++ b/tests/src/conc_increment.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <pthread.h>
 #include <unistd.h>
 #include <time.h>
 #include <stdlib.h>