diff --git a/pkg/template/helm_template.go b/pkg/template/helm_template.go
index 5870cef85..f451c0908 100644
--- a/pkg/template/helm_template.go
+++ b/pkg/template/helm_template.go
@@ -73,6 +73,15 @@ func (t *HelmTemplate) template(dirPath string, input io.Reader) exec.CmdRunResu
 		namespace = t.opts.Namespace
 	}
 
+	// name is passed to helm as a positional argument, so a leading '-'
+	// would be parsed as a helm flag instead of a release name.
+	if strings.HasPrefix(name, "-") {
+		return exec.NewCmdRunResultWithErr(fmt.Errorf("invalid helm template name '%s': must not start with '-'", name))
+	}
+	if strings.HasPrefix(namespace, "-") {
+		return exec.NewCmdRunResultWithErr(fmt.Errorf("invalid helm template namespace '%s': must not start with '-'", namespace))
+	}
+
 	args := []string{"template", name, chartPath, "--namespace", namespace, "--include-crds"}
 	vals := Values{t.opts.ValuesFrom, t.additionalValues, t.appContext, t.coreClient}
 
diff --git a/pkg/template/helm_template_test.go b/pkg/template/helm_template_test.go
new file mode 100644
index 000000000..c1006b102
--- /dev/null
+++ b/pkg/template/helm_template_test.go
@@ -0,0 +1,106 @@
+// Copyright 2024 The Carvel Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package template_test
+
+import (
+	"fmt"
+	"os"
+	goexec "os/exec"
+	"path/filepath"
+	"testing"
+
+	"carvel.dev/kapp-controller/pkg/apis/kappctrl/v1alpha1"
+	"carvel.dev/kapp-controller/pkg/exec"
+	"carvel.dev/kapp-controller/pkg/template"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	k8sfake "k8s.io/client-go/kubernetes/fake"
+)
+
+type recordingCmdRunner struct {
+	cmds []*goexec.Cmd
+}
+
+var _ exec.CmdRunner = &recordingCmdRunner{}
+
+func (r *recordingCmdRunner) Run(cmd *goexec.Cmd) error {
+	r.cmds = append(r.cmds, cmd)
+	return nil
+}
+
+func (r *recordingCmdRunner) RunWithCancel(cmd *goexec.Cmd, _ chan struct{}) error {
+	return r.Run(cmd)
+}
+
+func Test_HelmTemplate_NameAndNamespace(t *testing.T) {
+	appContext := template.AppContext{Name: "app-name", Namespace: "app-ns"}
+
+	testCases := []struct {
+		desc         string
+		opts         v1alpha1.AppTemplateHelmTemplate
+		expectedName string
+		expectedNs   string
+		expectedErr  string
+	}{
+		{desc: "defaults to app name and namespace", expectedName: "app-name", expectedNs: "app-ns"},
+		{desc: "custom name and namespace", opts: v1alpha1.AppTemplateHelmTemplate{Name: "my-release", Namespace: "my-ns"},
+			expectedName: "my-release", expectedNs: "my-ns"},
+		{desc: "name with dash in the middle", opts: v1alpha1.AppTemplateHelmTemplate{Name: "my-release-1"},
+			expectedName: "my-release-1", expectedNs: "app-ns"},
+		{desc: "name with leading double dash", opts: v1alpha1.AppTemplateHelmTemplate{Name: "--post-renderer=/bin/sh"},
+			expectedErr: "invalid helm template name '--post-renderer=/bin/sh': must not start with '-'"},
+		{desc: "name with leading single dash", opts: v1alpha1.AppTemplateHelmTemplate{Name: "-g"},
+			expectedErr: "invalid helm template name '-g': must not start with '-'"},
+		{desc: "namespace with leading dash", opts: v1alpha1.AppTemplateHelmTemplate{Namespace: "--debug"},
+			expectedErr: "invalid helm template namespace '--debug': must not start with '-'"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			cmdRunner := &recordingCmdRunner{}
+			helmTemplate := template.NewHelmTemplate(tc.opts, appContext, k8sfake.NewSimpleClientset(),
+				cmdRunner, template.AdditionalDownwardAPIValues{})
+
+			result, _ := helmTemplate.TemplateDir(t.TempDir())
+
+			if tc.expectedErr != "" {
+				assert.ErrorContains(t, result.Error, tc.expectedErr)
+				assert.Empty(t, cmdRunner.cmds, "helm should not be invoked")
+				return
+			}
+			require.NoError(t, result.Error)
+			require.Len(t, cmdRunner.cmds, 1)
+			args := cmdRunner.cmds[0].Args
+			assert.Equal(t, []string{"helm", "template", tc.expectedName}, args[:3])
+			assert.Equal(t, []string{"--namespace", tc.expectedNs}, args[4:6])
+		})
+	}
+}
+
+func Test_HelmTemplate_NameIsNotParsedAsHelmFlag(t *testing.T) {
+	rootDir := t.TempDir()
+	chartDir := filepath.Join(rootDir, "chart")
+	outsideFile := filepath.Join(rootDir, "outside.txt")
+	require.NoError(t, os.MkdirAll(filepath.Join(chartDir, "templates"), 0700))
+	require.NoError(t, os.WriteFile(filepath.Join(chartDir, "Chart.yaml"),
+		[]byte("apiVersion: v2\nname: test-chart\nversion: 0.1.0\n"), 0600))
+	require.NoError(t, os.WriteFile(filepath.Join(chartDir, "templates", "cm.yaml"), []byte(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: cm
+data:
+  value: {{ .Values.value | default "" | quote }}
+`), 0600))
+	require.NoError(t, os.WriteFile(outsideFile, []byte("content-outside-chart-dir"), 0600))
+
+	opts := v1alpha1.AppTemplateHelmTemplate{Name: fmt.Sprintf("--set-file=value=%s", outsideFile)}
+	helmTemplate := template.NewHelmTemplate(opts, template.AppContext{Name: "app", Namespace: "default"},
+		k8sfake.NewSimpleClientset(), exec.NewPlainCmdRunner(), template.AdditionalDownwardAPIValues{})
+
+	result, _ := helmTemplate.TemplateDir(chartDir)
+
+	assert.ErrorContains(t, result.Error, "must not start with '-'")
+	assert.NotContains(t, result.Stdout, "content-outside-chart-dir")
+}