diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElixirClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElixirClientCodegen.java
index 21ad9e70b144..dc850506eb68 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElixirClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElixirClientCodegen.java
@@ -52,7 +52,7 @@ public class ElixirClientCodegen extends DefaultCodegen implements CodegenConfig
     String supportedElixirVersion = "1.4";
     List<String> extraApplications = Arrays.asList(":logger");
     List<String> deps = Arrays.asList(
-            "{:tesla, \"~> 0.8\"}",
+            "{:tesla, \"~> 1.0.0\"}",
             "{:poison, \">= 1.0.0\"}"
     );
 
diff --git a/modules/openapi-generator/src/main/resources/elixir/connection.ex.mustache b/modules/openapi-generator/src/main/resources/elixir/connection.ex.mustache
index 052a9d357e47..82cfd90f48c9 100644
--- a/modules/openapi-generator/src/main/resources/elixir/connection.ex.mustache
+++ b/modules/openapi-generator/src/main/resources/elixir/connection.ex.mustache
@@ -8,8 +8,8 @@ defmodule {{moduleName}}.Connection do
 
   # Add any middleware here (authentication)
   plug Tesla.Middleware.BaseUrl, "{{{basePath}}}"
-  plug Tesla.Middleware.Headers, %{"User-Agent" => "Elixir"}
-  plug Tesla.Middleware.EncodeJson
+  plug Tesla.Middleware.Headers, [{"user-agent", "Elixir"}]
+  plug Tesla.Middleware.EncodeJson, engine: Poison
 
   {{#hasAuthMethods}}
   {{#authMethods}}
@@ -34,7 +34,7 @@ defmodule {{moduleName}}.Connection do
   @spec new(String.t) :: Tesla.Env.client
   def new(token) when is_binary(token) do
     Tesla.build_client([
-      {Tesla.Middleware.Headers,  %{"Authorization" => "Bearer #{token}"}}
+      {Tesla.Middleware.Headers,  [{"authorization", "Bearer #{token}"}]}
     ])
   end
 
diff --git a/modules/openapi-generator/src/main/resources/elixir/request_builder.ex.mustache b/modules/openapi-generator/src/main/resources/elixir/request_builder.ex.mustache
index 10afaba4ce58..bda2d25af960 100644
--- a/modules/openapi-generator/src/main/resources/elixir/request_builder.ex.mustache
+++ b/modules/openapi-generator/src/main/resources/elixir/request_builder.ex.mustache
@@ -87,7 +87,7 @@ defmodule {{moduleName}}.RequestBuilder do
   end
   def add_param(request, :headers, key, value) do
     request
-    |> Map.update(:headers, %{key => value}, &(Map.put(&1, key, value)))
+    |> Tesla.put_header(key, value)
   end
   def add_param(request, :file, name, path) do
     request
@@ -107,7 +107,7 @@ defmodule {{moduleName}}.RequestBuilder do
 
   ## Parameters
 
-  - arg1 (Tesla.Env.t | term) - The response object
+  - arg1 ({:ok, Tesla.Env.t} | term) - The response object
   - arg2 (:false | struct | [struct]) - The shape of the struct to deserialize into
 
   ## Returns
@@ -115,12 +115,16 @@ defmodule {{moduleName}}.RequestBuilder do
   {:ok, struct} on success
   {:error, term} on failure
   """
-  @spec decode(Tesla.Env.t | term()) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
-  def decode(%Tesla.Env{status: 200, body: body}), do: Poison.decode(body)
+  @spec decode({:ok, Tesla.Env.t} | term()) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
+  def decode({:ok, %Tesla.Env{status: 200, body: body}}), do: Poison.decode(body)
+  def decode(response), do: {:error, response}
+  def decode({:error, _} = error), do: error
   def decode(response), do: {:error, response}
 
-  @spec decode(Tesla.Env.t | term(), :false | struct() | [struct()]) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
-  def decode(%Tesla.Env{status: 200} = env, false), do: {:ok, env}
-  def decode(%Tesla.Env{status: 200, body: body}, struct), do: Poison.decode(body, as: struct)
+  @spec decode({:ok, Tesla.Env.t} | term(), :false | struct() | [struct()]) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
+  def decode({:ok, %Tesla.Env{status: 200}} = env, false), do: {:ok, env}
+  def decode({:ok, %Tesla.Env{status: 200, body: body}}, struct), do: Poison.decode(body, as: struct)
+  def decode({:ok, %Tesla.Env{} = response}, _struct), do: {:error, response}
+  def decode({:error, _} = error, _struct), do: error
   def decode(response, _struct), do: {:error, response}
 end
diff --git a/samples/client/petstore/elixir/lib/openapi_petstore/connection.ex b/samples/client/petstore/elixir/lib/openapi_petstore/connection.ex
index 834cc003d108..c44015b7f806 100644
--- a/samples/client/petstore/elixir/lib/openapi_petstore/connection.ex
+++ b/samples/client/petstore/elixir/lib/openapi_petstore/connection.ex
@@ -11,8 +11,8 @@ defmodule OpenapiPetstore.Connection do
 
   # Add any middleware here (authentication)
   plug Tesla.Middleware.BaseUrl, "http://petstore.swagger.io:80/v2"
-  plug Tesla.Middleware.Headers, %{"User-Agent" => "Elixir"}
-  plug Tesla.Middleware.EncodeJson
+  plug Tesla.Middleware.Headers, [{"user-agent", "Elixir"}]
+  plug Tesla.Middleware.EncodeJson, engine: Poison
 
   @doc """
   Configure a client connection using Basic authentication.
@@ -51,7 +51,7 @@ defmodule OpenapiPetstore.Connection do
   @spec new(String.t) :: Tesla.Env.client
   def new(token) when is_binary(token) do
     Tesla.build_client([
-      {Tesla.Middleware.Headers,  %{"Authorization" => "Bearer #{token}"}}
+      {Tesla.Middleware.Headers,  [{"authorization", "Bearer #{token}"}]}
     ])
   end
 
diff --git a/samples/client/petstore/elixir/lib/openapi_petstore/request_builder.ex b/samples/client/petstore/elixir/lib/openapi_petstore/request_builder.ex
index e81e72d1cf32..6d963fe445d0 100644
--- a/samples/client/petstore/elixir/lib/openapi_petstore/request_builder.ex
+++ b/samples/client/petstore/elixir/lib/openapi_petstore/request_builder.ex
@@ -90,7 +90,7 @@ defmodule OpenapiPetstore.RequestBuilder do
   end
   def add_param(request, :headers, key, value) do
     request
-    |> Map.update(:headers, %{key => value}, &(Map.put(&1, key, value)))
+    |> Tesla.put_header(key, value)
   end
   def add_param(request, :file, name, path) do
     request
@@ -110,7 +110,7 @@ defmodule OpenapiPetstore.RequestBuilder do
 
   ## Parameters
 
-  - arg1 (Tesla.Env.t | term) - The response object
+  - arg1 ({:ok, Tesla.Env.t} | term) - The response object
   - arg2 (:false | struct | [struct]) - The shape of the struct to deserialize into
 
   ## Returns
@@ -118,12 +118,14 @@ defmodule OpenapiPetstore.RequestBuilder do
   {:ok, struct} on success
   {:error, term} on failure
   """
-  @spec decode(Tesla.Env.t | term()) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
-  def decode(%Tesla.Env{status: 200, body: body}), do: Poison.decode(body)
+  @spec decode({:ok, Tesla.Env.t} | term()) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
+  def decode({:ok, %Tesla.Env{status: 200, body: body}}), do: Poison.decode(body)
   def decode(response), do: {:error, response}
+  def decode({:error, _} = error), do: error
 
-  @spec decode(Tesla.Env.t | term(), :false | struct() | [struct()]) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
-  def decode(%Tesla.Env{status: 200} = env, false), do: {:ok, env}
-  def decode(%Tesla.Env{status: 200, body: body}, struct), do: Poison.decode(body, as: struct)
+  @spec decode({:ok, Tesla.Env.t} | term(), :false | struct() | [struct()]) :: {:ok, struct()} | {:error, Tesla.Env.t} | {:error, term()}
+  def decode({:ok, %Tesla.Env{status: 200}} = env, false), do: {:ok, env}
+  def decode({:ok, %Tesla.Env{status: 200, body: body}}, struct), do: Poison.decode(body, as: struct)
+  def decode({:error, _} = error, _struct), do: error
   def decode(response, _struct), do: {:error, response}
 end
diff --git a/samples/client/petstore/elixir/mix.exs b/samples/client/petstore/elixir/mix.exs
index 469ffcee7827..74d94a93948c 100644
--- a/samples/client/petstore/elixir/mix.exs
+++ b/samples/client/petstore/elixir/mix.exs
@@ -29,7 +29,7 @@ defmodule OpenapiPetstore.Mixfile do
   # Type "mix help deps" for more examples and options
   defp deps do
     [
-      {:tesla, "~> 0.8"},
+      {:tesla, "~> 1.0.0"},
       {:poison, ">= 1.0.0"}
     ]
   end