diff --git a/internal/setup/setup.go b/internal/setup/setup.go
index 904cdb1e..7840d406 100644
--- a/internal/setup/setup.go
+++ b/internal/setup/setup.go
@@ -319,7 +319,7 @@ func readSlices(release *Release, baseDir, dirName string) error {
 
 type yamlRelease struct {
 	Format   string                 `yaml:"format"`
-	Archives map[string]yamlArchive `yaml:"archives`
+	Archives map[string]yamlArchive `yaml:"archives"`
 	Keyrings map[string]string      `yaml:"public-keys"`
 }
 
@@ -406,7 +406,7 @@ func parseRelease(baseDir, filePath string, data []byte) (*Release, error) {
 
 	yamlVar := yamlRelease{}
 	dec := yaml.NewDecoder(bytes.NewBuffer(data))
-	dec.KnownFields(true)
+	dec.KnownFields(false)
 	err := dec.Decode(&yamlVar)
 	if err != nil {
 		return nil, fmt.Errorf("%s: cannot parse release definition: %v", fileName, err)
@@ -479,7 +479,7 @@ func parsePackage(baseDir, pkgName, pkgPath string, data []byte) (*Package, erro
 
 	yamlPkg := yamlPackage{}
 	dec := yaml.NewDecoder(bytes.NewBuffer(data))
-	dec.KnownFields(true)
+	dec.KnownFields(false)
 	err := dec.Decode(&yamlPkg)
 	if err != nil {
 		return nil, fmt.Errorf("cannot parse package %q slice definitions: %v", pkgName, err)
diff --git a/internal/setup/setup_test.go b/internal/setup/setup_test.go
index 07a01862..81decfbb 100644
--- a/internal/setup/setup_test.go
+++ b/internal/setup/setup_test.go
@@ -925,6 +925,57 @@ var setupTests = []setupTest{{
 		`,
 	},
 	relerror: `chisel.yaml: cannot parse keyring "ubuntu-master": openpgp: invalid argument: no armored data found`,
+}, {
+	summary: "Extra fields in YAML are ignored (necessary for forward compatibility)",
+	input: map[string]string{
+		"chisel.yaml": `
+			format: chisel-v1
+			archives:
+				ubuntu:
+					version: 22.04
+					components: [main, other]
+					suites: [jammy, jammy-security]
+					madeUpKey1: whatever
+			madeUpKey2: whatever
+		`,
+		"slices/mydir/mypkg.yaml": `
+			package: mypkg
+			madeUpKey3: whatever
+			slices:
+				myslice:
+					madeUpKey4: whatever
+					contents:
+						/path: {madeUpKey5: whatever}
+		`,
+	},
+	release: &setup.Release{
+		DefaultArchive: "ubuntu",
+
+		Archives: map[string]*setup.Archive{
+			"ubuntu": {
+				Name:       "ubuntu",
+				Version:    "22.04",
+				Suites:     []string{"jammy", "jammy-security"},
+				Components: []string{"main", "other"},
+			},
+		},
+		Packages: map[string]*setup.Package{
+			"mypkg": {
+				Archive: "ubuntu",
+				Name:    "mypkg",
+				Path:    "slices/mydir/mypkg.yaml",
+				Slices: map[string]*setup.Slice{
+					"myslice": {
+						Package: "mypkg",
+						Name:    "myslice",
+						Contents: map[string]setup.PathInfo{
+							"/path": {Kind: "copy"},
+						},
+					},
+				},
+			},
+		},
+	},
 }}
 
 const defaultChiselYaml = `