diff --git a/lib/bundler/spec_set.rb b/lib/bundler/spec_set.rb
index 69dee36145..8d75c29420 100644
--- a/lib/bundler/spec_set.rb
+++ b/lib/bundler/spec_set.rb
@@ -83,6 +83,8 @@ module Bundler
     end
 
     def []=(key, value)
+      delete_by_name(key)
+
       add_spec(value)
     end