diff --git a/modules/packages/rubygems/metadata.go b/modules/packages/rubygems/metadata.go
index 7075b4233e3..357a7a11663 100644
--- a/modules/packages/rubygems/metadata.go
+++ b/modules/packages/rubygems/metadata.go
@@ -8,6 +8,8 @@ import (
 	"compress/gzip"
 	"io"
 	"regexp"
+	"slices"
+	"strings"
 	"sync"
 
 	"gitea.dev/modules/packages"
@@ -24,6 +26,8 @@ var (
 	ErrInvalidName = util.NewInvalidArgumentErrorf("package name is invalid")
 	// ErrInvalidVersion indicates an invalid version in the metadata.gz file
 	ErrInvalidVersion = util.NewInvalidArgumentErrorf("package version is invalid")
+	// ErrInvalidMetadata indicates metadata that would corrupt the generated index
+	ErrInvalidMetadata = util.NewInvalidArgumentErrorf("package metadata is invalid")
 )
 
 var globalVars = sync.OnceValue(func() (ret struct {
@@ -221,6 +225,19 @@ func parseMetadataFile(r io.Reader) (*Package, error) {
 		}
 	}
 
+	values := []string{m.Platform}
+	reqs := slices.Concat(m.RequiredRubyVersion, m.RequiredRubygemsVersion)
+	for _, dep := range slices.Concat(m.RuntimeDependencies, m.DevelopmentDependencies) {
+		values = append(values, dep.Name)
+		reqs = append(reqs, dep.Version...)
+	}
+	for _, req := range reqs {
+		values = append(values, req.Restriction, req.Version)
+	}
+	if slices.ContainsFunc(values, func(s string) bool { return strings.ContainsAny(s, "\r\n") }) {
+		return nil, ErrInvalidMetadata // the compact index is line-based, a line break would forge entries
+	}
+
 	return &Package{
 		Name:     spec.Name,
 		Version:  spec.Version.Version,
diff --git a/modules/packages/rubygems/metadata_test.go b/modules/packages/rubygems/metadata_test.go
index 8917bd2b36b..eba2cfd25cc 100644
--- a/modules/packages/rubygems/metadata_test.go
+++ b/modules/packages/rubygems/metadata_test.go
@@ -43,6 +43,19 @@ version:
 			assert.Nil(t, rp)
 		}
 	})
+
+	t.Run("LineBreakInIndexedMetadata", func(t *testing.T) {
+		for _, field := range []string{
+			`platform: "ruby\nx"`,
+			`dependencies: [{name: "d\nx"}]`,
+			`dependencies: [{name: d, requirement: {requirements: [[">=", {version: "1\nx"}]]}}]`,
+			`required_ruby_version: {requirements: [[">=", {version: "1\nx"}]]}`,
+		} {
+			rp, err := parseMetadataFile(test.CompressGzip("name: g\nversion:\n  version: 1\n" + field + "\n"))
+			assert.ErrorIs(t, err, ErrInvalidMetadata, field)
+			assert.Nil(t, rp)
+		}
+	})
 }
 
 func TestParseMetadataFile(t *testing.T) {