diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionTransitionProcedure.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionTransitionProcedure.java
index fb6090de849..9f1dd3863c5 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionTransitionProcedure.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionTransitionProcedure.java
@@ -424,9 +424,9 @@ public abstract class RegionTransitionProcedure
 
     // There is no rollback for assignment unless we cancel the operation by
     // dropping/disabling the table.
-    LOG.warn("Unhandled state {}; no rollback for assignment! Doing NOTHING!" +
-        " May need manual intervention. TODO: IS THIS WORKING? {}",
-        transitionState, this);
+    throw new UnsupportedOperationException("Unhandled state " + transitionState +
+        "; there is no rollback for assignment unless we cancel the operation by " +
+        "dropping/disabling the table");
   }
 
   protected abstract boolean isRollbackSupported(final RegionTransitionState state);