diff --git a/libraries/liblutil/signal.c b/libraries/liblutil/signal.c
index 230a265b95..64084c7eda 100644
--- a/libraries/liblutil/signal.c
+++ b/libraries/liblutil/signal.c
@@ -8,6 +8,7 @@
 #include "portable.h"
 
 #ifdef HAVE_SIGACTION
+#include <ac/string.h>
 #include <ac/signal.h>
 
 lutil_sig_t