diff --git a/cmd/image-builder/main.go b/cmd/image-builder/main.go
index 443b64d..899bd53 100644
--- a/cmd/image-builder/main.go
+++ b/cmd/image-builder/main.go
@@ -335,7 +335,7 @@ func cmdBuild(cmd *cobra.Command, args []string) error {
 	}
 
 	bootMode := res.ImgType.BootMode()
-	uploader, err := uploaderFor(cmd, res.ImgType.Name(), &bootMode)
+	uploader, err := uploaderFor(cmd, res.ImgType.Name(), res.ImgType.Arch().Name(), &bootMode)
 	if errors.Is(err, ErrUploadTypeUnsupported) || errors.Is(err, ErrUploadConfigNotProvided) {
 		err = nil
 	}
diff --git a/cmd/image-builder/upload.go b/cmd/image-builder/upload.go
index 4e46ce2..5357ac6 100644
--- a/cmd/image-builder/upload.go
+++ b/cmd/image-builder/upload.go
@@ -11,6 +11,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"github.com/osbuild/image-builder-cli/pkg/progress"
+	"github.com/osbuild/images/pkg/arch"
 	"github.com/osbuild/images/pkg/cloud"
 	"github.com/osbuild/images/pkg/cloud/awscloud"
 	"github.com/osbuild/images/pkg/platform"
@@ -62,17 +63,17 @@ func uploaderCheckWithProgress(pbar progress.ProgressBar, uploader cloud.Uploade
 	return uploader.Check(pw)
 }
 
-func uploaderFor(cmd *cobra.Command, typeOrCloud string, bootMode *platform.BootMode) (cloud.Uploader, error) {
+func uploaderFor(cmd *cobra.Command, typeOrCloud string, targetArch string, bootMode *platform.BootMode) (cloud.Uploader, error) {
 	switch typeOrCloud {
 	case "ami", "aws":
-		return uploaderForCmdAWS(cmd, bootMode)
+		return uploaderForCmdAWS(cmd, targetArch, bootMode)
 	default:
 		return nil, fmt.Errorf("%w: %q", ErrUploadTypeUnsupported, typeOrCloud)
 	}
 
 }
 
-func uploaderForCmdAWS(cmd *cobra.Command, bootMode *platform.BootMode) (cloud.Uploader, error) {
+func uploaderForCmdAWS(cmd *cobra.Command, targetArch string, bootMode *platform.BootMode) (cloud.Uploader, error) {
 	amiName, err := cmd.Flags().GetString("aws-ami-name")
 	if err != nil {
 		return nil, err
@@ -85,10 +86,6 @@ func uploaderForCmdAWS(cmd *cobra.Command, bootMode *platform.BootMode) (cloud.U
 	if err != nil {
 		return nil, err
 	}
-	targetArch, err := cmd.Flags().GetString("arch")
-	if err != nil {
-		return nil, err
-	}
 	if bootMode == nil {
 		// If unset, default to BOOT_HYBIRD which translated
 		// to "uefi-prefered" when registering the image.
@@ -127,6 +124,8 @@ func uploaderForCmdAWS(cmd *cobra.Command, bootMode *platform.BootMode) (cloud.U
 }
 
 func cmdUpload(cmd *cobra.Command, args []string) error {
+	imagePath := args[0]
+
 	uploadTo, err := cmd.Flags().GetString("to")
 	if err != nil {
 		return err
@@ -135,8 +134,18 @@ func cmdUpload(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("missing --to parameter, try --to=aws")
 	}
 
-	imagePath := args[0]
-	uploader, err := uploaderFor(cmd, uploadTo, nil)
+	targetArch, err := cmd.Flags().GetString("arch")
+	if err != nil {
+		return err
+	}
+	if targetArch == "" {
+		// we could try to inspect the image here and get a
+		// better guess
+		targetArch = arch.Current().String()
+		fmt.Fprintf(osStderr, "WARNING: no upload architecture specified, using %q (use --arch to override)\n", targetArch)
+	}
+
+	uploader, err := uploaderFor(cmd, uploadTo, targetArch, nil)
 	if err != nil {
 		return err
 	}
diff --git a/cmd/image-builder/upload_test.go b/cmd/image-builder/upload_test.go
index e75c8e2..66a1e10 100644
--- a/cmd/image-builder/upload_test.go
+++ b/cmd/image-builder/upload_test.go
@@ -12,6 +12,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/osbuild/images/pkg/arch"
 	"github.com/osbuild/images/pkg/cloud"
 	"github.com/osbuild/images/pkg/cloud/awscloud"
 	"github.com/osbuild/images/pkg/platform"
@@ -58,7 +59,7 @@ func TestUploadWithAWSMock(t *testing.T) {
 		targetArchArg      string
 		expectedUploadArch string
 	}{
-		{"", ""},
+		{"", "x86_64"},
 		{"aarch64", "aarch64"},
 	} {
 		var fa fakeAwsUploader
@@ -71,9 +72,11 @@ func TestUploadWithAWSMock(t *testing.T) {
 		})
 		defer restore()
 
-		var fakeStdout bytes.Buffer
+		var fakeStdout, fakeStderr bytes.Buffer
 		restore = main.MockOsStdout(&fakeStdout)
 		defer restore()
+		restore = main.MockOsStderr(&fakeStderr)
+		defer restore()
 
 		restore = main.MockOsArgs([]string{
 			"upload",
@@ -100,10 +103,19 @@ func TestUploadWithAWSMock(t *testing.T) {
 		assert.Equal(t, fakeDiskContent, fa.uploadAndRegisterRead.String())
 		// progress was rendered
 		assert.Contains(t, fakeStdout.String(), "--] 100.00%")
+
+		// warning was passed
+		if tc.targetArchArg == "" {
+			assert.Equal(t, fakeStderr.String(), `WARNING: no upload architecture specified, using "x86_64" (use --arch to override)`+"\n")
+		}
 	}
 }
 
 func TestUploadCmdlineErrors(t *testing.T) {
+	var fakeStderr bytes.Buffer
+	restore := main.MockOsStderr(&fakeStderr)
+	defer restore()
+
 	for _, tc := range []struct {
 		cmdline     []string
 		expectedErr string
@@ -183,7 +195,7 @@ func TestBuildAndUploadWithAWSMock(t *testing.T) {
 	assert.Equal(t, bucketName, "aws-bucket-2")
 	assert.Equal(t, amiName, "aws-ami-3")
 	expectedBootMode := platform.BOOT_HYBRID
-	assert.Equal(t, &awscloud.UploaderOptions{BootMode: &expectedBootMode}, uploadOpts)
+	assert.Equal(t, &awscloud.UploaderOptions{BootMode: &expectedBootMode, TargetArch: arch.Current().String()}, uploadOpts)
 	assert.Equal(t, 1, fa.checkCalls)
 	assert.Equal(t, 1, fa.uploadAndRegisterCalls)
 	assert.Equal(t, "fake-img-raw\n", fa.uploadAndRegisterRead.String())