diff --git a/lib/httpx/headers.rb b/lib/httpx/headers.rb
index 7a87f6a2..437733d8 100644
--- a/lib/httpx/headers.rb
+++ b/lib/httpx/headers.rb
@@ -67,7 +67,7 @@ module HTTPX
     #
     def [](field)
       a = @headers[downcased(field)] || return
-      a.join(",")
+      a.join(", ")
     end
 
     # sets +value+ (if not nil) as single value for the +field+ header.
diff --git a/test/headers_test.rb b/test/headers_test.rb
index d4a7ae18..53e48c8a 100644
--- a/test/headers_test.rb
+++ b/test/headers_test.rb
@@ -25,7 +25,7 @@ class HeadersTest < Minitest::Test
   def test_headers_add
     h1 = Headers.new("accept" => "text/html")
     h1.add("accept", "application/xhtml+xml")
-    assert h1["accept"] == "text/html,application/xhtml+xml", "unexpected header value"
+    assert h1["accept"] == "text/html, application/xhtml+xml", "unexpected header value"
     assert h1.get("accept") == %w[text/html application/xhtml+xml], "unexpected header value"
   end