diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index 564552a3b80..ad05dd6217d 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -293,6 +293,13 @@ def pretty_dep(dep, source = false)
     end
 
     def converge_sources
+      locked_gem = @locked_sources.find { |s| Source::Rubygems === s }
+      actual_gem = @sources.find { |s| Source::Rubygems === s }
+
+      if locked_gem && actual_gem
+        locked_gem.merge_remotes actual_gem
+      end
+
       @sources.map! do |source|
         @locked_sources.find { |s| s == source } || source
       end
diff --git a/lib/bundler/source.rb b/lib/bundler/source.rb
index 75a26a84aec..31555893f36 100644
--- a/lib/bundler/source.rb
+++ b/lib/bundler/source.rb
@@ -129,6 +129,13 @@ def add_remote(source)
         @remotes << normalize_uri(source)
       end
 
+      def merge_remotes(source)
+        @remotes = []
+        source.remotes.each do |r|
+          add_remote r.to_s
+        end
+      end
+
     private
 
       def cached_gem(spec)
diff --git a/spec/install/gems/flex_spec.rb b/spec/install/gems/flex_spec.rb
index 8a5c1a3dbed..e8520715814 100644
--- a/spec/install/gems/flex_spec.rb
+++ b/spec/install/gems/flex_spec.rb
@@ -220,7 +220,7 @@
       G
 
       gemfile <<-G
-        source "file:://#{gem_repo1}"
+        source "file://#{gem_repo1}"
         gem "rack", "0.9.1"
         gem "rack-obama"
       G
@@ -240,4 +240,33 @@
       bundle "update rack"
     end
   end
+
+  describe "when adding a new source" do
+    it "updates the lockfile" do
+      build_repo2
+      install_gemfile <<-G
+        source "file://#{gem_repo1}"
+        gem "rack"
+      G
+      install_gemfile <<-G
+        source "file://#{gem_repo1}"
+        source "file://#{gem_repo2}"
+        gem "rack"
+      G
+
+      lockfile_should_be <<-L
+      GEM
+        remote: file:#{gem_repo1}/
+        remote: file:#{gem_repo2}/
+        specs:
+          rack (1.0.0)
+
+      PLATFORMS
+        ruby
+
+      DEPENDENCIES
+        rack
+      L
+    end
+  end
 end