diff --git a/packageurl.go b/packageurl.go
index 8ebc6c3..518b0e1 100644
--- a/packageurl.go
+++ b/packageurl.go
@@ -957,10 +957,7 @@ func validCustomRules(p PackageURL) error {
 			return errors.New("a chrome-extension version must be 1 to 4 dot-separated integers")
 		}
 	case TypeCpan:
-		// It MUST be written uppercase and is required.
-		if p.Namespace == "" {
-			return errors.New("a cpan purl must have a namespace")
-		}
+		// It MUST be written uppercase.
 		if strings.ToUpper(p.Namespace) != p.Namespace {
 			return errors.New("a cpan purl namespace must use uppercase characters")
 		}
diff --git a/testdata/purl-spec b/testdata/purl-spec
index 1eed5b6..9d6b901 160000
--- a/testdata/purl-spec
+++ b/testdata/purl-spec
@@ -1 +1 @@
-Subproject commit 1eed5b60c6abca0f07d049e5f88c21ae25a1f407
+Subproject commit 9d6b901c9905392e7eb208697c708fe5796efbba