diff --git a/bin/normalize.rb b/bin/normalize.rb
index bf9593f..4629796 100755
--- a/bin/normalize.rb
+++ b/bin/normalize.rb
@@ -78,6 +78,10 @@
 sources.each do |s|
   begin
     s.normalize
+  rescue ::InetData::Source::Base::NotImplemented
+    # logger.log("Warning: Source #{s.name} does not implement normalize()")
+  rescue ::Interrupt
+    logger.log("Error: Source #{s.name} was interrupted: #{$!.class} #{$!} #{$!.backtrace}")
   rescue ::Exception
     logger.log("Error: Source #{s.name} threw an exception: #{$!.class} #{$!} #{$!.backtrace}")
   end
diff --git a/lib/inetdata/source/base.rb b/lib/inetdata/source/base.rb
index 69c568f..89e9bb5 100644
--- a/lib/inetdata/source/base.rb
+++ b/lib/inetdata/source/base.rb
@@ -2,6 +2,9 @@ module InetData
   module Source
     class Base
 
+      class NotImplemented < ::RuntimeError
+      end
+
       @@have_inetdata_parsers = nil
 
       VALID_HOSTNAME = /^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])(\.([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9]))*$/
@@ -57,11 +60,11 @@ def reports_path
       end
 
       def download
-        raise RuntimeError.new, "Download not implemented for source #{self.name}"
+        raise NotImplemented
       end
 
       def normalize
-        raise RuntimeError.new, "Normalize not implemented for source #{self.name}"
+        raise NotImplemented
       end
 
       def validate_domain(dname)