diff --git a/server/modules/routing/avrorouter/rpl.cc b/server/modules/routing/avrorouter/rpl.cc
index 70c0fefe5..1155dd5b3 100644
--- a/server/modules/routing/avrorouter/rpl.cc
+++ b/server/modules/routing/avrorouter/rpl.cc
@@ -1116,7 +1116,7 @@ const char* keywords[] =
     NULL
 };
 
-static bool token_is_keyword(const char* tok, int len)
+static bool token_is_keyword(const char* tok, size_t len)
 {
     for (int i = 0; keywords[i]; i++)
     {