diff --git a/lib/req/steps.ex b/lib/req/steps.ex
index 79eb432..108288d 100644
--- a/lib/req/steps.ex
+++ b/lib/req/steps.ex
@@ -1191,7 +1191,6 @@ defmodule Req.Steps do
         |> Keyword.put_new(:datetime, DateTime.utc_now())
         # aws_credentials returns this key so let's ignore it
         |> Keyword.drop([:credential_provider])
-        |> maybe_put_aws_service(request.url)
 
       Req.Request.validate_options(aws_options, [
         :access_key_id,
@@ -1205,6 +1204,16 @@ defmodule Req.Steps do
         :expires
       ])
 
+      unless aws_options[:access_key_id] do
+        raise ArgumentError, "missing :access_key_id in :aws_sigv4 option"
+      end
+
+      unless aws_options[:secret_access_key] do
+        raise ArgumentError, "missing :secret_access_key in :aws_sigv4 option"
+      end
+
+      aws_options = ensure_aws_service(aws_options, request.url)
+
       {body, options} =
         case request.body do
           nil ->
@@ -1242,14 +1251,14 @@ defmodule Req.Steps do
     end
   end
 
-  defp maybe_put_aws_service(options, url) do
+  defp ensure_aws_service(options, url) do
     if options[:service] do
       options
     else
       if service = detect_aws_service(url) do
         Keyword.put(options, :service, service)
       else
-        options
+        raise ArgumentError, "missing :service in :aws_sigv4 option"
       end
     end
   end
diff --git a/test/req/steps_test.exs b/test/req/steps_test.exs
index 7af4501..f29b3c2 100644
--- a/test/req/steps_test.exs
+++ b/test/req/steps_test.exs
@@ -566,6 +566,36 @@ defmodule Req.StepsTest do
 
       assert Req.put!(req).body == "ok"
     end
+
+    test "missing :access_key_id" do
+      req = Req.new(aws_sigv4: [])
+
+      assert_raise ArgumentError, "missing :access_key_id in :aws_sigv4 option", fn ->
+        Req.get(req)
+      end
+    end
+
+    test "missing :secret_access_key" do
+      req = Req.new(aws_sigv4: [access_key_id: "foo"])
+
+      assert_raise ArgumentError, "missing :secret_access_key in :aws_sigv4 option", fn ->
+        Req.get(req)
+      end
+    end
+
+    test "missing :service" do
+      req =
+        Req.new(
+          aws_sigv4: [
+            access_key_id: "foo",
+            secret_access_key: "bar"
+          ]
+        )
+
+      assert_raise ArgumentError, "missing :service in :aws_sigv4 option", fn ->
+        Req.get(req)
+      end
+    end
   end
 
   ## Response steps