diff --git a/libao2/ao_polyp.c b/libao2/ao_polyp.c
index 5f9f72eff8..e037070058 100644
--- a/libao2/ao_polyp.c
+++ b/libao2/ao_polyp.c
@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <string.h>
 
 #include <polyp/polyplib.h>
 #include <polyp/polyplib-error.h>