diff --git a/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java b/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
index ca9fc61..819b02f 100644
--- a/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
@@ -92,7 +92,7 @@
     public static Ip4Prefix valueOf(String address) {
         final String[] parts = address.split("/");
         if (parts.length != 2) {
-            String msg = "Malformed IPv4 prefix string: " + address + "." +
+            String msg = "Malformed IPv4 prefix string: " + address + ". " +
                 "Address must take form \"x.x.x.x/y\"";
             throw new IllegalArgumentException(msg);
         }
diff --git a/utils/misc/src/main/java/org/onlab/packet/Ip6Prefix.java b/utils/misc/src/main/java/org/onlab/packet/Ip6Prefix.java
index ca9985e..b9b45fa 100644
--- a/utils/misc/src/main/java/org/onlab/packet/Ip6Prefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/Ip6Prefix.java
@@ -80,7 +80,7 @@
     public static Ip6Prefix valueOf(String address) {
         final String[] parts = address.split("/");
         if (parts.length != 2) {
-            String msg = "Malformed IPv6 prefix string: " + address + "." +
+            String msg = "Malformed IPv6 prefix string: " + address + ". " +
                 "Address must take form " +
                 "\"xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/y\"";
             throw new IllegalArgumentException(msg);
diff --git a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
index c97c2e3..2a89762 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
@@ -178,7 +178,7 @@
     public static IpPrefix valueOf(String address) {
         final String[] parts = address.split("/");
         if (parts.length != 2) {
-            String msg = "Malformed IP prefix string: " + address + "." +
+            String msg = "Malformed IP prefix string: " + address + ". " +
                 "Address must take form \"x.x.x.x/y\" or " +
                 "\"xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/y\"";
             throw new IllegalArgumentException(msg);