diff --git a/src/gsm/auth_core.c b/src/gsm/auth_core.c
index d0c9f1c..f790ff5 100644
--- a/src/gsm/auth_core.c
+++ b/src/gsm/auth_core.c
@@ -22,6 +22,7 @@
 
 #include <errno.h>
 #include <stdint.h>
+#include <string.h>
 
 #include <osmocom/core/utils.h>
 #include <osmocom/core/linuxlist.h>