diff --git a/base/src/main/java/org/mozilla/jss/netscape/security/x509/RevocationReason.java b/base/src/main/java/org/mozilla/jss/netscape/security/x509/RevocationReason.java
index 7988b3b94..e455c5a92 100644
--- a/base/src/main/java/org/mozilla/jss/netscape/security/x509/RevocationReason.java
+++ b/base/src/main/java/org/mozilla/jss/netscape/security/x509/RevocationReason.java
@@ -88,6 +88,9 @@ public static RevocationReason valueOf(int reason) {
     }
 
     public static RevocationReason valueOf(String string) {
+        if (string == null) {
+            return null;
+        }
         return LABELS.get(string.toLowerCase());
     }