diff --git a/bundler/lib/bundler/fetcher/index.rb b/bundler/lib/bundler/fetcher/index.rb
index 363d3c0ac652..08b041897eb3 100644
--- a/bundler/lib/bundler/fetcher/index.rb
+++ b/bundler/lib/bundler/fetcher/index.rb
@@ -19,8 +19,7 @@ def specs(_gem_names)
           raise BadAuthenticationError, remote_uri if remote_uri.userinfo
           raise AuthenticationRequiredError, remote_uri
         else
-          Bundler.ui.trace e
-          raise HTTPError, "Could not fetch specs from #{display_uri}"
+          raise HTTPError, "Could not fetch specs from #{display_uri} due to underlying error <#{e.message}>"
         end
       end
 
diff --git a/bundler/spec/bundler/fetcher/index_spec.rb b/bundler/spec/bundler/fetcher/index_spec.rb
index dd695b53b7fa..b8ce46321e1b 100644
--- a/bundler/spec/bundler/fetcher/index_spec.rb
+++ b/bundler/spec/bundler/fetcher/index_spec.rb
@@ -90,7 +90,7 @@
       before { allow(Bundler).to receive(:ui).and_return(double(:trace => nil)) }
 
       it "should raise a Bundler::HTTPError" do
-        expect { subject.specs(gem_names) }.to raise_error(Bundler::HTTPError, "Could not fetch specs from http://sample_uri.com")
+        expect { subject.specs(gem_names) }.to raise_error(Bundler::HTTPError, "Could not fetch specs from http://sample_uri.com due to underlying error <You get an error, you get an error! (http://sample_uri.com)>")
       end
     end
   end
diff --git a/bundler/spec/realworld/mirror_probe_spec.rb b/bundler/spec/realworld/mirror_probe_spec.rb
index 626092c7ebee..a2b5c89150db 100644
--- a/bundler/spec/realworld/mirror_probe_spec.rb
+++ b/bundler/spec/realworld/mirror_probe_spec.rb
@@ -74,10 +74,10 @@
       bundle :install, :artifice => nil, :raise_on_error => false
 
       expect(out).to include("Fetching source index from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Could not fetch specs from #{mirror}")
+      expect(err).to include("Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
     end
 
     it "prints each error and warning on a new line" do
@@ -90,10 +90,10 @@
 
       expect(out).to include "Fetching source index from #{mirror}/"
       expect(err).to include <<-EOS.strip
-Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}/
-Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}/
-Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}/
-Could not fetch specs from #{mirror}/
+Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>
+Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>
+Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>
+Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>
       EOS
     end
   end
@@ -112,10 +112,10 @@
       bundle :install, :artifice => nil, :raise_on_error => false
 
       expect(out).to include("Fetching source index from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}")
-      expect(err).to include("Could not fetch specs from #{mirror}")
+      expect(err).to include("Retrying fetcher due to error (2/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Retrying fetcher due to error (3/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Retrying fetcher due to error (4/4): Bundler::HTTPError Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
+      expect(err).to include("Could not fetch specs from #{mirror}/ due to underlying error <Errno::ECONNREFUSED: Failed to open TCP connection to #{host}:#{@mirror_port} (Connection refused - connect(2) for \"#{host}\" port #{@mirror_port}) (#{mirror}/specs.4.8.gz)>")
     end
   end
 
@@ -138,7 +138,7 @@ def setup_server
   end
 
   def setup_mirror
-    mirror_port = find_unused_port
-    @mirror_uri = "http://#{host}:#{mirror_port}"
+    @mirror_port = find_unused_port
+    @mirror_uri = "http://#{host}:#{@mirror_port}"
   end
 end