diff --git a/internal/chart/v3/lint/rules/values.go b/internal/chart/v3/lint/rules/values.go
index a91e70363..9ebf405c4 100644
--- a/internal/chart/v3/lint/rules/values.go
+++ b/internal/chart/v3/lint/rules/values.go
@@ -23,6 +23,8 @@ import (
 	"path/filepath"
 	"strings"
 
+	yamlv2 "go.yaml.in/yaml/v2"
+
 	"helm.sh/helm/v4/internal/chart/v3/lint/support"
 	"helm.sh/helm/v4/pkg/chart/common"
 	"helm.sh/helm/v4/pkg/chart/common/util"
@@ -89,10 +91,16 @@ func validateValuesFile(valuesPath string, overrides map[string]any, skipSchemaV
 	return nil
 }
 
-// isDuplicateKeyError checks if an error is related to duplicate YAML keys
+// isDuplicateKeyError checks if an error is related to duplicate YAML keys.
 func isDuplicateKeyError(err error) bool {
-	errStr := err.Error()
-	return strings.Contains(errStr, "already set in map") ||
-		strings.Contains(errStr, "already defined") ||
-		strings.Contains(errStr, "duplicate")
+	var typeErr *yamlv2.TypeError
+	if !errors.As(err, &typeErr) {
+		return false
+	}
+	for _, e := range typeErr.Errors {
+		if strings.Contains(e, "already set in map") {
+			return true
+		}
+	}
+	return false
 }
diff --git a/internal/chart/v3/lint/rules/values_test.go b/internal/chart/v3/lint/rules/values_test.go
index 54c7e6457..0324930ed 100644
--- a/internal/chart/v3/lint/rules/values_test.go
+++ b/internal/chart/v3/lint/rules/values_test.go
@@ -17,11 +17,14 @@ limitations under the License.
 package rules
 
 import (
+	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	yamlv2 "go.yaml.in/yaml/v2"
 
 	"helm.sh/helm/v4/internal/test/ensure"
 )
@@ -181,3 +184,58 @@ func createTestingSchema(t *testing.T, dir string) string {
 	}
 	return schemafile
 }
+
+func TestIsDuplicateKeyError(t *testing.T) {
+	tests := []struct {
+		name     string
+		err      error
+		expected bool
+	}{
+		{
+			name:     "duplicate key error",
+			err:      &yamlv2.TypeError{Errors: []string{`line 2: key "key" already set in map`}},
+			expected: true,
+		},
+		{
+			name:     "wrapped duplicate key error",
+			err:      fmt.Errorf("error converting YAML to JSON: %w", &yamlv2.TypeError{Errors: []string{`line 2: key "key" already set in map`}}),
+			expected: true,
+		},
+		{
+			name:     "non-duplicate key error",
+			err:      errors.New("some other error"),
+			expected: false,
+		},
+		{
+			name:     "type error but not duplicate-key related",
+			err:      &yamlv2.TypeError{Errors: []string{"cannot unmarshal !!seq into map[string]interface {}"}},
+			expected: false,
+		},
+		{
+			name:     "nil error",
+			err:      nil,
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isDuplicateKeyError(tt.err)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func TestValidateValuesFileDuplicateKeys(t *testing.T) {
+	duplicateYaml := `key: value1
+key: value2
+`
+	tmpdir := ensure.TempFile(t, "values.yaml", []byte(duplicateYaml))
+	valfile := filepath.Join(tmpdir, "values.yaml")
+
+	err := validateValuesFile(valfile, map[string]any{}, false)
+	if err == nil {
+		t.Fatal("expected values file with duplicate keys to fail parsing")
+	}
+	assert.Contains(t, err.Error(), "contains duplicate keys")
+}