diff --git a/lib/madison.rb b/lib/madison.rb
index <HASH>..<HASH> 100644
--- a/lib/madison.rb
+++ b/lib/madison.rb
@@ -10,12 +10,12 @@ module Madison
     end
 
     def get_abbrev(name)
-      raise ArgumentError("Argument must be a string") unless name.is_a? String
+      validate_arg(name)
       state_abbrevs[name.downcase]
     end
 
     def get_name(abbrev)
-      raise ArgumentError("Argument must be a string") unless abbrev.is_a? String
+      validate_arg(abbrev)
       state_names[abbrev.downcase]
     end
 
@@ -34,6 +34,10 @@ module Madison
         map 
       end
     end
+
+    def validate_arg(arg)
+      raise ArgumentError, "Argument '#{arg}' must be a string" unless arg.is_a? String
+    end
   end
 
   @map = Map.new
Fixed bug; slightly refactored ArgumentError error raising