diff --git a/lib/ex_aws/sts/parsers.ex b/lib/ex_aws/sts/parsers.ex
index b892d14..19102d3 100644
--- a/lib/ex_aws/sts/parsers.ex
+++ b/lib/ex_aws/sts/parsers.ex
@@ -1,142 +1,137 @@
-if Code.ensure_loaded?(SweetXml) do
-  defmodule ExAws.STS.Parsers do
-    import SweetXml, only: [sigil_x: 2]
-
-    def parse({:ok, %{body: xml} = resp}, :assume_role) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//AssumeRoleResponse",
-          access_key_id: ~x"./AssumeRoleResult/Credentials/AccessKeyId/text()"s,
-          secret_access_key: ~x"./AssumeRoleResult/Credentials/SecretAccessKey/text()"s,
-          session_token: ~x"./AssumeRoleResult/Credentials/SessionToken/text()"s,
-          expiration: ~x"./AssumeRoleResult/Credentials/Expiration/text()"s,
-          assumed_role_id: ~x"./AssumeRoleResult/AssumedRoleUser/AssumedRoleId/text()"s,
-          assumed_role_arn: ~x"./AssumeRoleResult/AssumedRoleUser/Arn/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :assume_role_with_web_identity) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//AssumeRoleWithWebIdentityResponse",
-          access_key_id: ~x"./AssumeRoleWithWebIdentityResult/Credentials/AccessKeyId/text()"s,
-          secret_access_key:
-            ~x"./AssumeRoleWithWebIdentityResult/Credentials/SecretAccessKey/text()"s,
-          session_token: ~x"./AssumeRoleWithWebIdentityResult/Credentials/SessionToken/text()"s,
-          expiration: ~x"./AssumeRoleWithWebIdentityResult/Credentials/Expiration/text()"s,
-          assumed_role_id:
-            ~x"./AssumeRoleWithWebIdentityResult/AssumedRoleUser/AssumedRoleId/text()"s,
-          assumed_role_arn: ~x"./AssumeRoleWithWebIdentityResult/AssumedRoleUser/Arn/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :get_access_key_info) do
-      parsed_body =
-        SweetXml.xpath(xml, ~x"//GetAccessKeyInfoResponse",
-          account: ~x"./GetAccessKeyInfoResult/Account/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :assume_role_with_s_a_m_l) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//AssumeRoleWithSAMLResponse",
-          access_key_id: ~x"./AssumeRoleResult/Credentials/AccessKeyId/text()"s,
-          secret_access_key: ~x"./AssumeRoleResult/Credentials/SecretAccessKey/text()"s,
-          session_token: ~x"./AssumeRoleResult/Credentials/SessionToken/text()"s,
-          expiration: ~x"./AssumeRoleResult/Credentials/Expiration/text()"s,
-          assumed_role_id: ~x"./AssumeRoleResult/AssumedRoleUser/AssumedRoleId/text()"s,
-          assumed_role_arn: ~x"./AssumeRoleResult/AssumedRoleUser/Arn/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :get_caller_identity) do
-      parsed_body =
-        SweetXml.xpath(xml, ~x"//GetCallerIdentityResponse",
-          arn: ~x"./GetCallerIdentityResult/Arn/text()"s,
-          user_id: ~x"./GetCallerIdentityResult/UserId/text()"s,
-          account: ~x"./GetCallerIdentityResult/Account/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :get_federation_token) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//GetFederationTokenResponse",
-          access_key_id: ~x"./GetFederationTokenResult/Credentials/AccessKeyId/text()"s,
-          secret_access_key: ~x"./GetFederationTokenResult/Credentials/SecretAccessKey/text()"s,
-          session_token: ~x"./GetFederationTokenResult/Credentials/SessionToken/text()"s,
-          expiration: ~x"./GetFederationTokenResult/Credentials/Expiration/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:ok, %{body: xml} = resp}, :get_session_token) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//GetSessionTokenResponse",
-          access_key_id: ~x"./GetSessionTokenResult/Credentials/AccessKeyId/text()"s,
-          secret_access_key: ~x"./GetSessionTokenResult/Credentials/SecretAccessKey/text()"s,
-          session_token: ~x"./GetSessionTokenResult/Credentials/SessionToken/text()"s,
-          expiration: ~x"./GetSessionTokenResult/Credentials/Expiration/text()"s,
-          request_id: request_id_xpath()
-        )
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    def parse({:error, {type, http_status_code, %{body: xml}}}, _) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//ErrorResponse",
-          request_id: ~x"./RequestId/text()"s,
-          type: ~x"./Error/Type/text()"s,
-          code: ~x"./Error/Code/text()"s,
-          message: ~x"./Error/Message/text()"s,
-          detail: ~x"./Error/Detail/text()"s
-        )
-
-      {:error, {type, http_status_code, parsed_body}}
-    end
-
-    def parse(val, _), do: val
-
-    def parse({:ok, %{body: xml} = resp}, :decode_authorization_message, config) do
-      parsed_body =
-        xml
-        |> SweetXml.xpath(~x"//DecodeAuthorizationMessageResponse",
-          decoded_message: ~x"./DecodedMessage/text()"s,
-          request_id: ~x"./RequestId/text()"s
-        )
-        |> Map.update!(:decoded_message, fn msg -> config[:json_codec].decode!(msg) end)
-
-      {:ok, Map.put(resp, :body, parsed_body)}
-    end
-
-    defp request_id_xpath do
-      ~x"./ResponseMetadata/RequestId/text()"s
-    end
+defmodule ExAws.STS.Parsers do
+  alias ExAws.STS.Parsers.XML
+
+  import XML, only: [sigil_x: 2]
+
+  def parse({:ok, %{body: xml} = resp}, :assume_role) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//AssumeRoleResponse",
+        access_key_id: ~x"./AssumeRoleResult/Credentials/AccessKeyId/text()"s,
+        secret_access_key: ~x"./AssumeRoleResult/Credentials/SecretAccessKey/text()"s,
+        session_token: ~x"./AssumeRoleResult/Credentials/SessionToken/text()"s,
+        expiration: ~x"./AssumeRoleResult/Credentials/Expiration/text()"s,
+        assumed_role_id: ~x"./AssumeRoleResult/AssumedRoleUser/AssumedRoleId/text()"s,
+        assumed_role_arn: ~x"./AssumeRoleResult/AssumedRoleUser/Arn/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
   end
-else
-  defmodule ExAws.STS.Parsers do
-    def parse(val, _), do: val
-    def parse(val, _, _), do: val
+
+  def parse({:ok, %{body: xml} = resp}, :assume_role_with_web_identity) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//AssumeRoleWithWebIdentityResponse",
+        access_key_id: ~x"./AssumeRoleWithWebIdentityResult/Credentials/AccessKeyId/text()"s,
+        secret_access_key:
+          ~x"./AssumeRoleWithWebIdentityResult/Credentials/SecretAccessKey/text()"s,
+        session_token: ~x"./AssumeRoleWithWebIdentityResult/Credentials/SessionToken/text()"s,
+        expiration: ~x"./AssumeRoleWithWebIdentityResult/Credentials/Expiration/text()"s,
+        assumed_role_id:
+          ~x"./AssumeRoleWithWebIdentityResult/AssumedRoleUser/AssumedRoleId/text()"s,
+        assumed_role_arn: ~x"./AssumeRoleWithWebIdentityResult/AssumedRoleUser/Arn/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:ok, %{body: xml} = resp}, :get_access_key_info) do
+    parsed_body =
+      XML.xpath(xml, ~x"//GetAccessKeyInfoResponse",
+        account: ~x"./GetAccessKeyInfoResult/Account/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:ok, %{body: xml} = resp}, :assume_role_with_s_a_m_l) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//AssumeRoleWithSAMLResponse",
+        access_key_id: ~x"./AssumeRoleResult/Credentials/AccessKeyId/text()"s,
+        secret_access_key: ~x"./AssumeRoleResult/Credentials/SecretAccessKey/text()"s,
+        session_token: ~x"./AssumeRoleResult/Credentials/SessionToken/text()"s,
+        expiration: ~x"./AssumeRoleResult/Credentials/Expiration/text()"s,
+        assumed_role_id: ~x"./AssumeRoleResult/AssumedRoleUser/AssumedRoleId/text()"s,
+        assumed_role_arn: ~x"./AssumeRoleResult/AssumedRoleUser/Arn/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:ok, %{body: xml} = resp}, :get_caller_identity) do
+    parsed_body =
+      XML.xpath(xml, ~x"//GetCallerIdentityResponse",
+        arn: ~x"./GetCallerIdentityResult/Arn/text()"s,
+        user_id: ~x"./GetCallerIdentityResult/UserId/text()"s,
+        account: ~x"./GetCallerIdentityResult/Account/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:ok, %{body: xml} = resp}, :get_federation_token) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//GetFederationTokenResponse",
+        access_key_id: ~x"./GetFederationTokenResult/Credentials/AccessKeyId/text()"s,
+        secret_access_key: ~x"./GetFederationTokenResult/Credentials/SecretAccessKey/text()"s,
+        session_token: ~x"./GetFederationTokenResult/Credentials/SessionToken/text()"s,
+        expiration: ~x"./GetFederationTokenResult/Credentials/Expiration/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:ok, %{body: xml} = resp}, :get_session_token) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//GetSessionTokenResponse",
+        access_key_id: ~x"./GetSessionTokenResult/Credentials/AccessKeyId/text()"s,
+        secret_access_key: ~x"./GetSessionTokenResult/Credentials/SecretAccessKey/text()"s,
+        session_token: ~x"./GetSessionTokenResult/Credentials/SessionToken/text()"s,
+        expiration: ~x"./GetSessionTokenResult/Credentials/Expiration/text()"s,
+        request_id: request_id_xpath()
+      )
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  def parse({:error, {type, http_status_code, %{body: xml}}}, _) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//ErrorResponse",
+        request_id: ~x"./RequestId/text()"s,
+        type: ~x"./Error/Type/text()"s,
+        code: ~x"./Error/Code/text()"s,
+        message: ~x"./Error/Message/text()"s,
+        detail: ~x"./Error/Detail/text()"s
+      )
+
+    {:error, {type, http_status_code, parsed_body}}
+  end
+
+  def parse(val, _), do: val
+
+  def parse({:ok, %{body: xml} = resp}, :decode_authorization_message, config) do
+    parsed_body =
+      xml
+      |> XML.xpath(~x"//DecodeAuthorizationMessageResponse",
+        decoded_message: ~x"./DecodedMessage/text()"s,
+        request_id: ~x"./RequestId/text()"s
+      )
+      |> Map.update!(:decoded_message, fn msg -> config[:json_codec].decode!(msg) end)
+
+    {:ok, Map.put(resp, :body, parsed_body)}
+  end
+
+  defp request_id_xpath do
+    ~x"./ResponseMetadata/RequestId/text()"s
   end
 end
diff --git a/lib/ex_aws/sts/parsers/xml.ex b/lib/ex_aws/sts/parsers/xml.ex
new file mode 100644
index 0000000..c78a641
--- /dev/null
+++ b/lib/ex_aws/sts/parsers/xml.ex
@@ -0,0 +1,19 @@
+defmodule ExAws.STS.Parsers.XML do
+  @moduledoc false
+
+  def xpath(parent, spec, subspec) do
+    xml_module().xpath(parent, spec, subspec)
+  rescue
+    _ in UndefinedFunctionError ->
+      raise "Dependency sweet_xml is required for role based authentication"
+  end
+
+  def sigil_x(path, modifiers) do
+    xml_module().sigil_x(path, modifiers)
+  rescue
+    _ in UndefinedFunctionError ->
+      raise "Dependency sweet_xml is required for role based authentication"
+  end
+
+  defp xml_module, do: Application.get_env(:ex_aws_sts, :xml_module, SweetXml)
+end
diff --git a/test/lib/parsers_test.exs b/test/lib/parsers_test.exs
index 7151918..daff707 100644
--- a/test/lib/parsers_test.exs
+++ b/test/lib/parsers_test.exs
@@ -1,5 +1,5 @@
 defmodule ExAws.STS.ParsersTest do
-  use ExUnit.Case, async: true
+  use ExUnit.Case, async: false
 
   alias ExAws.STS.Parsers
 
@@ -40,4 +40,22 @@ defmodule ExAws.STS.ParsersTest do
       end
     end
   end
+
+  describe "when sweet_xml is not installed" do
+    setup do
+      Application.put_env(:ex_aws_sts, :xml_module, MissingSweetXml)
+
+      on_exit(fn ->
+        Application.delete_env(:ex_aws_sts, :xml_module)
+      end)
+    end
+
+    for {action, arity} <- @actions do
+      test "raises missing sweet_xml error for `:#{action}`" do
+        assert_raise RuntimeError,
+                     "Dependency sweet_xml is required for role based authentication",
+                     fn -> parse_mock_response(unquote(action), unquote(arity)) end
+      end
+    end
+  end
 end