diff --git a/src/isinetaddr.c b/src/isinetaddr.c
index c5ceb71..09adf25 100644
--- a/src/isinetaddr.c
+++ b/src/isinetaddr.c
@@ -32,9 +32,13 @@ isinetaddr(const char *str)
         return 0;
       }
     } else if (isdigit(str[l])) {
-      buf[k++] = str[l];
-      buf[k] = '\0';
-      i++;
+      if (k == 3) {
+        return 0;
+      } else {
+        buf[k++] = str[l];
+        buf[k] = '\0';
+        i++;
+      }
     } else {
       return 0;
     }
diff --git a/test/isinetaddr_test.c b/test/isinetaddr_test.c
index f0a9a13..0c5e555 100644
--- a/test/isinetaddr_test.c
+++ b/test/isinetaddr_test.c
@@ -17,7 +17,7 @@ const char *invalid[] = {
   "192.168.1.1.",
   "192.168.1.1..",
   "192.168.1.1a",
-  //"555555555555555555555555555555555555",
+  "555555555555555555555555555555555555",
   "",
   NULL
 };