diff --git a/clients/gax/lib/google_api/gax/connection.ex b/clients/gax/lib/google_api/gax/connection.ex
index 1b7e95edfe..5473916785 100644
--- a/clients/gax/lib/google_api/gax/connection.ex
+++ b/clients/gax/lib/google_api/gax/connection.ex
@@ -33,7 +33,7 @@ defmodule GoogleApi.Gax.Connection do
         )
       )
 
-      plug(Tesla.Middleware.DecompressResponse, [])
+      plug(Tesla.Middleware.DecompressResponse, max_body_size: :infinity)
 
       plug(Tesla.Middleware.EncodeJson, engine: Poison)
 
@@ -182,7 +182,7 @@ defmodule GoogleApi.Gax.Connection do
       nil -> body
       _   -> Tesla.Multipart.add_field(
         body,
-        :metadata,
+        "metadata",
         Poison.encode!(meta),
         headers: [{:"Content-Type", "application/json"}]
       )
@@ -193,7 +193,7 @@ defmodule GoogleApi.Gax.Connection do
         {res, type} = try_encode_multipart_field(data, meta)
         Tesla.Multipart.add_field(
           b,
-          body_name,
+          to_string(body_name),
           res,
           headers: [{:"Content-Type", type}]
         )
diff --git a/clients/gax/mix.exs b/clients/gax/mix.exs
index b654b6cc49..000e7e1294 100644
--- a/clients/gax/mix.exs
+++ b/clients/gax/mix.exs
@@ -27,7 +27,6 @@ defmodule GoogleApi.Gax.MixProject do
   defp deps() do
     [
       {:tesla, "~> 1.2"},
-      {:mime, "~> 1.0"},
       {:poison, ">= 3.0.0 and < 5.0.0"},
       {:ex_doc, "~> 0.16", only: :dev},
       {:dialyxir, "~> 0.5", only: [:dev], runtime: false}
diff --git a/clients/gax/test/gax/api_test.exs b/clients/gax/test/gax/api_test.exs
index fbcc574e14..34a77bfd35 100644
--- a/clients/gax/test/gax/api_test.exs
+++ b/clients/gax/test/gax/api_test.exs
@@ -35,7 +35,7 @@ defmodule Gax.ApiTest do
     mock(fn %{
               method: :get,
               url: "https://example.com/v1/stores/store-1/pets",
-              headers: [{"x-goog-api-client", ^api_client}]
+              headers: [{"x-goog-api-client", ^api_client}, {"accept-encoding", "gzip, deflate, identity"}]
             } ->
       %Tesla.Env{status: 200, body: @pets_json}
     end)
@@ -61,7 +61,7 @@ defmodule Gax.ApiTest do
     mock(fn %{
               method: :get,
               url: "https://example.com/v1/stores/store-1/pets",
-              headers: [{"x-goog-api-client", ^api_client}]
+              headers: [{"x-goog-api-client", ^api_client}, {"accept-encoding", "gzip, deflate, identity"}]
             } ->
       %Tesla.Env{status: 200, body: @pets_json_compressed,
                  headers: [{"content-encoding", "gzip"}]}
diff --git a/clients/gax/test/gax/connection_test.exs b/clients/gax/test/gax/connection_test.exs
index 1c2fef131f..8bfe2dfdfe 100644
--- a/clients/gax/test/gax/connection_test.exs
+++ b/clients/gax/test/gax/connection_test.exs
@@ -143,6 +143,24 @@ defmodule Gax.ConnectionTest do
     end)
   end
 
+  # Regression test for tesla >= 1.18.3 compatibility: Tesla.Multipart.add_field/4
+  # now requires binary field names and raises on atoms, so build_body/3 must
+  # stringify the metadata key and every body param name.
+  test "multipart field names are strings, not atoms" do
+    request =
+      Request.new()
+      |> Request.add_param(:body, :metadata, %{foo: "bar"})
+      |> Request.add_param(:body, :data, %{baz: "qux"})
+      |> Connection.build_request()
+
+    body = %Tesla.Multipart{} = Keyword.get(request, :body)
+    names = Enum.map(body.parts, fn part -> Keyword.get(part.dispositions, :name) end)
+
+    assert Enum.all?(names, &is_binary/1)
+    assert "metadata" in names
+    assert "data" in names
+  end
+
   test "creates api client header without library version" do
     request =
       Request.new()