diff --git a/t/test-dtmf-detect.c b/t/test-dtmf-detect.c
index 20874f29f..5e38dc039 100644
--- a/t/test-dtmf-detect.c
+++ b/t/test-dtmf-detect.c
@@ -8,6 +8,7 @@
 #include <spandsp/logging.h>
 #include <spandsp/dtmf.h>
 #include <glib.h>
+#include <string.h>
 
 static unsigned char samples[] = {
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,