diff --git a/lib/isc/heap.c b/lib/isc/heap.c
index fb2477259a..4c11ddbcc7 100644
--- a/lib/isc/heap.c
+++ b/lib/isc/heap.c
@@ -26,6 +26,7 @@
  */
 
 #include <stdlib.h>
+#include <string.h>
 
 #include <isc/assertions.h>
 #include <isc/heap.h>