diff --git a/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java b/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
index eb0f58f0cbf8..d91852f6bc9c 100644
--- a/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
+++ b/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
@@ -285,7 +285,8 @@ private void parseSeverity(String arg) {
         try {
           severity = Severity.valueOf(parts.get(1));
         } catch (IllegalArgumentException e) {
-          throw new InvalidCommandLineOptionException("invalid flag: " + arg);
+          throw new InvalidCommandLineOptionException(
+              "invalid flag: " + arg + " (" + parts.get(1) + " was not a valid severity)");
         }
       }
       severityMap.put(checkName, severity);