diff --git a/lib/httpx/adapters/faraday.rb b/lib/httpx/adapters/faraday.rb
index 3e26591c..6df2d78e 100644
--- a/lib/httpx/adapters/faraday.rb
+++ b/lib/httpx/adapters/faraday.rb
@@ -210,9 +210,12 @@ module Faraday
         if parallel?(env)
           handler = env[:parallel_manager].enqueue(env)
           handler.on_response do |response|
-            response.raise_for_status
-            save_response(env, response.status, response.body.to_s, response.headers, response.reason) do |response_headers|
-              response_headers.merge!(response.headers)
+            if response.is_a?(::HTTPX::Response)
+              save_response(env, response.status, response.body.to_s, response.headers, response.reason) do |response_headers|
+                response_headers.merge!(response.headers)
+              end
+            else
+              save_response(env, 0, "", {}, nil)
             end
           end
           return handler
@@ -229,6 +232,7 @@ module Faraday
         request.response_on_data = env.request.on_data if env.request.stream_response?
 
         response = session.request(request)
+        # do not call #raise_for_status for HTTP 4xx or 5xx, as faraday has a middleware for that.
         response.raise_for_status unless response.is_a?(::HTTPX::Response)
         save_response(env, response.status, response.body.to_s, response.headers, response.reason) do |response_headers|
           response_headers.merge!(response.headers)
diff --git a/test/adapters/faraday_test.rb b/test/adapters/faraday_test.rb
index 73e492a9..44f5022b 100644
--- a/test/adapters/faraday_test.rb
+++ b/test/adapters/faraday_test.rb
@@ -29,6 +29,21 @@ class FaradayTest < Minitest::Test
     assert_equal "OK", resp2.reason_phrase
   end
 
+  def test_adapter_in_parallel_errors
+    resp1 = nil
+
+    connection = create_connection
+    connection.in_parallel do
+      resp1 = connection.get("http://wfijojsfsoijf")
+      assert connection.in_parallel?
+      assert_nil resp1.reason_phrase
+    end
+    assert !connection.in_parallel?
+    assert_equal 0, resp1.status
+    assert_nil resp1.reason_phrase
+    assert_equal "", resp1.body
+  end
+
   def test_adapter_get_handles_compression
     res = get(build_path("/gzip"))
     assert JSON.parse(res.body.to_s)["gzipped"]