diff --git a/lib/index.mjs b/lib/index.mjs
index d276e77..6c21560 100644
--- a/lib/index.mjs
+++ b/lib/index.mjs
@@ -119,6 +119,11 @@ export function parseRegistryName(hostname) {
   // registry rejects sends a tab to a page saying it does not exist.
   const LABEL = /^[a-z0-9]{1,63}$/;
   if (!LABEL.test(label) || !LABEL.test(tld)) return null;
+  // Both halves numeric is refused by the registry — several parsers read a
+  // two-part dotted number as an abbreviated IPv4 literal, so `1.420` is
+  // genuinely ambiguous where `blue.420` is not. Accepting it here would send
+  // a tab to a parking page for a name the registry can never register.
+  if (/^\d+$/.test(label) && /^\d+$/.test(tld)) return null;
   return { label, tld };
 }
 
diff --git a/test/resolve.test.mjs b/test/resolve.test.mjs
index 2afade7..83c906e 100644
--- a/test/resolve.test.mjs
+++ b/test/resolve.test.mjs
@@ -241,4 +241,9 @@ test("dashes are not part of a Moshpit name", () => {
   }
   assert.deepEqual(parseRegistryName("california.oranges"), { label: "california", tld: "oranges" });
   assert.deepEqual(parseRegistryName("blue.420"), { label: "blue", tld: "420" });
+  // Both halves numeric is refused by the registry (reads as an abbreviated
+  // IPv4 literal), so the port refuses it too — otherwise a tab lands on a
+  // parking page for a name the registry can never register.
+  assert.equal(parseRegistryName("1.420"), null, "1.420");
+  assert.equal(parseRegistryName("420.187"), null, "420.187");
 });