diff --git a/java/com/google/gerrit/server/restapi/change/Rebase.java b/java/com/google/gerrit/server/restapi/change/Rebase.java
index 2e2f565..eed0896 100644
--- a/java/com/google/gerrit/server/restapi/change/Rebase.java
+++ b/java/com/google/gerrit/server/restapi/change/Rebase.java
@@ -161,7 +161,8 @@
 
     Base base = rebaseUtil.parseBase(rsrc, str);
     if (base == null) {
-      throw new ResourceConflictException("base revision is missing: " + str);
+      throw new ResourceConflictException(
+          "base revision is missing from the destination branch: " + str);
     }
     PatchSet.Id baseId = base.patchSet().getId();
     if (change.getId().equals(baseId.getParentKey())) {