diff --git a/src/iscidraddr.c b/src/iscidraddr.c
index 1ce8f93..ccd01ae 100644
--- a/src/iscidraddr.c
+++ b/src/iscidraddr.c
@@ -9,11 +9,12 @@ int
 iscidraddr(const char *str)
 {
   size_t offset = 0;
-  size_t len = (str == NULL ? 0 : strnlen(str, 20));
+  size_t len = (str == NULL ? 0 : strnlen(str, 16));
 
   for(size_t i = 0; i < len; i++) {
     if(str[i] == '/') {
       offset = i;
+      break;
     }
   }
   if (offset == 0) {
diff --git a/test/iscidraddr_test.c b/test/iscidraddr_test.c
index 6a888b6..95440fb 100644
--- a/test/iscidraddr_test.c
+++ b/test/iscidraddr_test.c
@@ -11,6 +11,7 @@ const char *valid[] = {
   /* valid cidr notation */
   "10.0.0.1/8", "10.0.0.1/16",
   "10.0.0.1/24", "10.0.0.1/32",
+  "255.255.255.255/32"
 };
 
 const char *invalid[] = {