diff --git a/lib/bundler/dsl.rb b/lib/bundler/dsl.rb
index 8983ef3e2b..1ae19a46e9 100644
--- a/lib/bundler/dsl.rb
+++ b/lib/bundler/dsl.rb
@@ -124,19 +124,17 @@ module Bundler
             raise GemfileError, "You cannot specify the same gem twice with different version requirements.\n" \
                             "You specified: #{current.name} (#{current.requirement}) and #{dep.name} (#{dep.requirement})" \
                              "#{update_prompt}"
+          elsif current.source != dep.source
+            return if dep.type == :development
+            raise GemfileError, "You cannot specify the same gem twice coming from different sources.\n" \
+                            "You specified that #{dep.name} (#{dep.requirement}) should come from " \
+                            "#{current.source || "an unspecified source"} and #{dep.source}\n"
           else
             Bundler.ui.warn "Your Gemfile lists the gem #{current.name} (#{current.requirement}) more than once.\n" \
                             "You should probably keep only one of them.\n" \
                             "Remove any duplicate entries and specify the gem only once.\n" \
                             "While it's not a problem now, it could cause errors if you change the version of one of them later."
           end
-
-          if current.source != dep.source
-            return if dep.type == :development
-            raise GemfileError, "You cannot specify the same gem twice coming from different sources.\n" \
-                            "You specified that #{dep.name} (#{dep.requirement}) should come from " \
-                            "#{current.source || "an unspecified source"} and #{dep.source}\n"
-          end
         end
       end
 
diff --git a/spec/bundler/install/gemfile/sources_spec.rb b/spec/bundler/install/gemfile/sources_spec.rb
index 62cad6800f..89c812e5d5 100644
--- a/spec/bundler/install/gemfile/sources_spec.rb
+++ b/spec/bundler/install/gemfile/sources_spec.rb
@@ -1255,6 +1255,32 @@ RSpec.describe "bundle install with gems on multiple sources" do
     end
   end
 
+  context "when Gemfile overrides a gemspec development dependency to change the default source" do
+    before do
+      build_repo4 do
+        build_gem "bar"
+      end
+
+      build_lib("gemspec_test", :path => tmp.join("gemspec_test")) do |s|
+        s.add_development_dependency "bar"
+      end
+
+      install_gemfile <<-G, :artifice => "compact_index"
+        source "https://gem.repo1"
+
+        source "https://gem.repo4" do
+          gem "bar"
+        end
+
+        gemspec :path => "#{tmp.join("gemspec_test")}"
+      G
+    end
+
+    it "does not print warnings" do
+      expect(err).to be_empty
+    end
+  end
+
   it "doesn't update version when a gem uses a source block but a higher version from another source is already installed locally" do
     build_repo2 do
       build_gem "example", "0.1.0"