diff --git a/CIDRUtils.java b/CIDRUtils.java
index d564209..e9c1c5a 100644
--- a/CIDRUtils.java
+++ b/CIDRUtils.java
@@ -60,7 +60,7 @@ public CIDRUtils(String cidr) throws UnknownHostException {
 
             calculate();
         } else {
-            throw new IllegalArgumentException("not an valid CIDR format!");
+            throw new IllegalArgumentException("not a valid CIDR format!");
         }
     }