diff --git a/utils/misc/src/main/java/org/onlab/packet/IPv4.java b/utils/misc/src/main/java/org/onlab/packet/IPv4.java
index e54e9e7..28f6a48 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IPv4.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IPv4.java
@@ -32,10 +32,10 @@
     public static final byte PROTOCOL_ICMP = 0x1;
     public static final byte PROTOCOL_TCP = 0x6;
     public static final byte PROTOCOL_UDP = 0x11;
-    public static Map<Byte, Class<? extends IPacket>> protocolClassMap;
+    public static Map<Byte, Class<? extends IPacket>> protocolClassMap =
+            new HashMap<>();
 
     static {
-        IPv4.protocolClassMap = new HashMap<Byte, Class<? extends IPacket>>();
         IPv4.protocolClassMap.put(IPv4.PROTOCOL_ICMP, ICMP.class);
         IPv4.protocolClassMap.put(IPv4.PROTOCOL_TCP, TCP.class);
         IPv4.protocolClassMap.put(IPv4.PROTOCOL_UDP, UDP.class);