2 files changed, 8 insertions, 1 deletions
diff --git a/ext/psych/lib/psych/exception.rb b/ext/psych/lib/psych/exception.rb
index 04a9a906a4..d7469a4b30 100644
--- a/ext/psych/lib/psych/exception.rb
+++ b/ext/psych/lib/psych/exception.rb
@@ -13,6 +13,13 @@ module Psych
     end
   end
 
+  # Subclasses `BadAlias` for backwards compatibility
+  class AnchorNotDefined < BadAlias
+    def initialize anchor_name
+      super "An alias referenced an unknown anchor: #{anchor_name}"
+    end
+  end
+
   class DisallowedClass < Exception
     def initialize action, klass_name
       super "Tried to #{action} unspecified class: #{klass_name}"
diff --git a/ext/psych/lib/psych/visitors/to_ruby.rb b/ext/psych/lib/psych/visitors/to_ruby.rb
index 0bf5198ccc..cce5daf3bb 100644
--- a/ext/psych/lib/psych/visitors/to_ruby.rb
+++ b/ext/psych/lib/psych/visitors/to_ruby.rb
@@ -323,7 +323,7 @@ module Psych
       end
 
       def visit_Psych_Nodes_Alias o
-        @st.fetch(o.anchor) { raise BadAlias, "Unknown alias: #{o.anchor}" }
+        @st.fetch(o.anchor) { raise AnchorNotDefined, o.anchor }
       end
 
       private