diff --git a/README.md b/README.md
index 1e496f1..32f5345 100644
--- a/README.md
+++ b/README.md
@@ -44,7 +44,7 @@ Start a mix session with `iex -S mix` and type the following instructions
 path = Path.expand("~/workspace/elixir-docker-guide")
 
 {:ok, image_id} = Path.join([path, "Dockerfile"]) |>
-  ExDockerBuild.DockerfileParser.parse!() |>
+  ExDockerBuild.DockerfileParser.parse_file!() |>
   ExDockerBuild.DockerBuild.build(path)
 ```
 
@@ -68,7 +68,7 @@ $> mkdir ~/test
 path = Path.expand("./test/fixtures")
 
 {:ok, image_id} = Path.join([path, "Dockerfile_bind.dockerfile"]) |>
-  ExDockerBuild.DockerfileParser.parse!() |>
+  ExDockerBuild.DockerfileParser.parse_file!() |>
   ExDockerBuild.DockerBuild.build(path)
 ```
 
diff --git a/lib/ex_docker_build/dockerfile_parser.ex b/lib/ex_docker_build/dockerfile_parser.ex
index 404998b..ad437f3 100644
--- a/lib/ex_docker_build/dockerfile_parser.ex
+++ b/lib/ex_docker_build/dockerfile_parser.ex
@@ -3,15 +3,18 @@ defmodule ExDockerBuild.DockerfileParser do
   @continuation ~r/^.*\\\s*$/
   @instruction ~r/^\s*(\w+)\s+(.*)$/
 
-  @spec parse!(Path.t() | String.t()) :: list(String.t()) | no_return()
-  def parse!(path_or_content) do
-    content =
-      if File.exists?(path_or_content) do
-        File.read!(path_or_content)
-      else
-        path_or_content
-      end
+  @spec parse_file!(Path.t()) :: list(String.t()) | no_return()
+  def parse_file!(path) do
+    path
+    |> File.read!()
+    |> do_parse()
+  end
+
+  @spec parse_content!(String.t()) :: list(String.t()) | no_return()
+  def parse_content!(content), do: do_parse(content)
 
+  @spec do_parse(String.t()) :: list(String.t())
+  defp do_parse(content) do
     {parsed_lines, _} =
       content
       |> String.split("\n")
diff --git a/test/dockerfile_parser_test.exs b/test/dockerfile_parser_test.exs
index 393fca5..b5bec2f 100644
--- a/test/dockerfile_parser_test.exs
+++ b/test/dockerfile_parser_test.exs
@@ -10,7 +10,7 @@ defmodule ExDockerBuild.DockerfileParserTest do
 
   def parse(base_dir, file) do
     Path.join([base_dir, file])
-    |> Parser.parse!()
+    |> Parser.parse_file!()
   end
 
   test "parses correctly a simple Dockerfile", %{base_dir: base_dir} do
@@ -67,7 +67,7 @@ defmodule ExDockerBuild.DockerfileParserTest do
     CMD ["cat", "/data/myfile.txt"]
     """
 
-    result = Parser.parse!(content)
+    result = Parser.parse_content!(content)
 
     assert result == [
              {"FROM", "elixir:1.7.3"},