diff --git a/README.md b/README.md
index aa585f86..770ea319 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,7 @@ end
 defp deps do
   [
     {:excoveralls, "~> 0.10", only: :test},
+    {:hackney, "~> 1.16", only: :test} # only required if posting to the coveralls.io service
   ]
 end
 ```
diff --git a/lib/excoveralls/poster.ex b/lib/excoveralls/poster.ex
index fba50f3d..e357e85a 100644
--- a/lib/excoveralls/poster.ex
+++ b/lib/excoveralls/poster.ex
@@ -22,40 +22,56 @@ defmodule ExCoveralls.Poster do
     end
   end
 
-  defp send_file(file_name, options) do
-    Application.ensure_all_started(:hackney)
-    endpoint = options[:endpoint] || "https://coveralls.io"
-
-    response =
-      :hackney.request(
-        :post,
-        "#{endpoint}/api/v1/jobs",
-        [],
-        {:multipart,
-         [
-           {:file, file_name, {"form-data", [{"name", "json_file"}, {"filename", file_name}]},
-            [{"Content-Type", "gzip/json"}]}
-         ]},
-        [{:recv_timeout, 10_000}]
-      )
+  if Code.ensure_loaded?(:hackney) do
+    defp send_file(file_name, options) do
+      Application.ensure_all_started(:hackney)
+      endpoint = options[:endpoint] || "https://coveralls.io"
 
-    case response do
-      {:ok, status_code, _, _} when status_code in 200..299 ->
-        {:ok, "Successfully uploaded the report to '#{endpoint}'."}
+      response =
+        :hackney.request(
+          :post,
+          "#{endpoint}/api/v1/jobs",
+          [],
+          {:multipart,
+           [
+             {:file, file_name, {"form-data", [{"name", "json_file"}, {"filename", file_name}]},
+              [{"Content-Type", "gzip/json"}]}
+           ]},
+          [{:recv_timeout, 10_000}]
+        )
+
+      case response do
+        {:ok, status_code, _, _} when status_code in 200..299 ->
+          {:ok, "Successfully uploaded the report to '#{endpoint}'."}
+
+        {:ok, status_code, _, client} ->
+          {:ok, body} = :hackney.body(client)
 
-      {:ok, status_code, _, client} ->
-        {:ok, body} = :hackney.body(client)
+          {:error,
+           "Failed to upload the report to '#{endpoint}' (reason: status_code = #{status_code}, body = #{
+             body
+           })."}
+
+        {:error, reason} when reason in [:timeout, :connect_timeout] ->
+          {:ok,
+           "Unable to upload the report to '#{endpoint}' due to a timeout. Not failing the build."}
+
+        {:error, reason} ->
+          {:error, "Failed to upload the report to '#{endpoint}' (reason: #{inspect(reason)})."}
+      end
+    end
+  else
+    defp send_file(_, _) do
+      raise """
+      missing :hackney dependency
 
-        {:error,
-         "Failed to upload the report to '#{endpoint}' (reason: status_code = #{status_code}, body = #{
-           body
-         })."}
+      ExCoveralls requires :hackney to post to the coveralls.io service.
 
-      {:error, reason}  when reason in [:timeout, :connect_timeout] ->
-        {:ok, "Unable to upload the report to '#{endpoint}' due to a timeout. Not failing the build."}
+      Please add :hackney to your mix.exs :deps list and run:
 
-      {:error, reason} ->
-        {:error, "Failed to upload the report to '#{endpoint}' (reason: #{inspect(reason)})."}
+          mix deps.get
+          mix deps.clean --build excoveralls
+      """
     end
   end
 end
diff --git a/mix.exs b/mix.exs
index f36e009b..d39e5d02 100644
--- a/mix.exs
+++ b/mix.exs
@@ -39,7 +39,7 @@ defmodule ExCoveralls.Mixfile do
   def deps do
     [
       {:jason, "~> 1.0"},
-      {:hackney, "~> 1.16"},
+      {:hackney, "~> 1.16", optional: true},
       {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
       {:meck, "~> 0.8", only: :test},
       {:mock, "~> 0.3.6", only: :test}