diff --git a/etc/scripts/purl_type_definition.py b/etc/scripts/purl_type_definition.py
index 09fe5123..bd70e95b 100644
--- a/etc/scripts/purl_type_definition.py
+++ b/etc/scripts/purl_type_definition.py
@@ -254,3 +254,11 @@ class NamespaceDefinition(PurlComponentDefinition):
         ),
         title="Namespace requirement",
     )
+    known_values: Optional[list[str]] = Field(
+        None,
+        description=(
+            "Optional set of known values for this namespace. If provided, the namespace value"
+            " SHOULD be one of these."
+        ),
+        title="Known values",
+    )
diff --git a/schemas/purl-type-definition.schema.json b/schemas/purl-type-definition.schema.json
index cd48883d..9b6687c8 100644
--- a/schemas/purl-type-definition.schema.json
+++ b/schemas/purl-type-definition.schema.json
@@ -162,6 +162,15 @@
               "$ref": "#/definitions/prohibited_requirement"
             }
           ]
+        },
+        "registered_values": {
+          "title": "Registered values",
+          "description": "Optional set of known namespace values for this package type. If provided, the namespace value should be one of these.",
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "uniqueItems": true
         }
       },
       "allOf": [
diff --git a/types/deb-definition.json b/types/deb-definition.json
index 7d767b6f..e0b0856d 100644
--- a/types/deb-definition.json
+++ b/types/deb-definition.json
@@ -12,7 +12,11 @@
     "native_name": "vendor",
     "case_sensitive": false,
     "note": "The namespace is the \"vendor\" name such as \"debian\" or \"ubuntu\". It is not case sensitive and must be lowercased.",
-    "requirement": "required"
+    "requirement": "required",
+    "registered_values": [
+      "debian",
+      "ubuntu"
+    ]
   },
   "name_definition": {
     "requirement": "required",
diff --git a/types/rpm-definition.json b/types/rpm-definition.json
index 653cfde8..07e41ec0 100644
--- a/types/rpm-definition.json
+++ b/types/rpm-definition.json
@@ -12,7 +12,18 @@
     "case_sensitive": false,
     "native_name": "vendor",
     "note": "The namespace is the vendor such as Fedora or OpenSUSE. It is not case sensitive and must be lowercased.",
-    "requirement": "required"
+    "requirement": "required",
+    "registered_values": [
+      "redhat",
+      "centos",
+      "fedora",
+      "almalinux",
+      "rockylinux",
+      "opensuse",
+      "oraclelinux",
+      "amazonlinux",
+      "azurelinux"
+    ]
   },
   "name_definition": {
     "requirement": "required",