diff --git a/specs-go/v1/layout.go b/specs-go/v1/layout.go
index a54a461c5..c44486bfb 100644
--- a/specs-go/v1/layout.go
+++ b/specs-go/v1/layout.go
@@ -14,8 +14,15 @@
 
 package v1
 
+import "regexp"
+
 // ImageLayout is the structure in the "oci-layout" file, found in the root
 // of an OCI Image-layout directory.
 type ImageLayout struct {
 	Version string `json:"imageLayoutVersion"`
 }
+
+var (
+	// RefsRegexp matches requirement of image-layout 'refs' charset.
+	RefsRegexp = regexp.MustCompile(`^[a-zA-Z0-9-._]+$`)
+)