diff --git a/__tests__/auth.test.ts b/__tests__/auth.test.ts
index 4500de15..a18693df 100644
--- a/__tests__/auth.test.ts
+++ b/__tests__/auth.test.ts
@@ -913,9 +913,28 @@ describe('auth tests', () => {
     ]);
   });
 
+  it.each([
+    'https://repo.example.com:8443',
+    'https://repo.example.com:8443/maven',
+    'https://[2001:db8::1]',
+    'https://[2001:db8::1]/maven',
+    'https://[2001:db8::1]:8443',
+    'https://[2001:db8::1]:8443/maven'
+  ])('preserves the complete mirror URL %s with an explicit selector', url => {
+    expect(
+      auth.parseMavenMirrors([`private:${url}:external:http:*,!internal`])
+    ).toEqual([{id: 'private', url, mirrorOf: 'external:http:*,!internal'}]);
+  });
+
   it.each([
     'private',
     'private:https://repo.example.com',
+    'private:https://repo.example.com:8443',
+    'private:https://repo.example.com:8443/maven',
+    'private:https://[2001:db8::1]',
+    'private:https://[2001:db8::1]/maven',
+    'private:https://[2001:db8::1]:8443',
+    'private:https://[2001:db8::1]:8443/maven',
     ':https://repo.example.com:*',
     'private::*',
     'private:https://repo.example.com:',
diff --git a/dist/setup/81.index.js b/dist/setup/81.index.js
index 28c50048..1dc4058b 100644
--- a/dist/setup/81.index.js
+++ b/dist/setup/81.index.js
@@ -234,15 +234,15 @@ function parseMavenMirrors(entries) {
         }
         const separator = entry.indexOf(':');
         const remainder = entry.slice(separator + 1).trim();
-        // Consume the URL scheme before looking for the selector delimiter. Selector
-        // tokens may themselves contain colons (external:* and external:http:*).
-        const scheme = /^[A-Za-z][A-Za-z0-9+.-]*:/.exec(remainder)?.[0] ?? '';
-        const fields = /^(.*?):((?:\s*!?external:(?:http:)?\*\s*|[^:,]*)(?:,(?:\s*!?external:(?:http:)?\*\s*|[^:,]*))*)$/.exec(remainder.slice(scheme.length));
+        // Protect scheme/authority colons (including IPv6 and ports) before
+        // finding the selector, which may itself contain external:http:*.
+        const urlPrefix = /^[A-Za-z][A-Za-z0-9+.-]*:(?:\/\/(?:[^/?#@\s]*@)?(?:\[[^\]]+\]|[^:/?#\s]+)(?::\d+(?=[/?#:\s]|$))?)?/.exec(remainder)?.[0] ?? '';
+        const fields = /^(.*?):((?:\s*!?external:(?:http:)?\*\s*|[^:,]*)(?:,(?:\s*!?external:(?:http:)?\*\s*|[^:,]*))*)$/.exec(remainder.slice(urlPrefix.length));
         if (separator < 0 || !fields) {
             throw new Error(`Invalid mvn-mirrors entry at line ${index + 1}. Expected format: mirror-id:mirror-url:mirror-of`);
         }
         const id = entry.slice(0, separator).trim();
-        const url = `${scheme}${fields[1]}`.trim();
+        const url = `${urlPrefix}${fields[1]}`.trim();
         const mirrorOf = fields[2].trim();
         if (!id || !url || !mirrorOf) {
             throw new Error(`Invalid mvn-mirrors entry at line ${index + 1}. mirror-id, mirror URL, and mirror-of are required`);
diff --git a/docs/advanced-usage.md b/docs/advanced-usage.md
index 488d1efb..11799679 100644
--- a/docs/advanced-usage.md
+++ b/docs/advanced-usage.md
@@ -1099,8 +1099,9 @@ Unlike repository profiles, mirrors replace the destination Maven contacts.
 The Central controls described above do not redirect arbitrary POM repositories.
 
 Each nonblank line has the format `mirror-id:mirror-url:mirror-of`. IDs must be
-unique within this input. URL schemes and ports, and colons in `mirrorOf`
-selectors, are preserved. For example:
+unique within this input. URL schemes, ports, IPv6 addresses, and colons in
+`mirrorOf` selectors are preserved. An explicit `mirror-of` field is required
+after the complete URL, including any port. For example:
 
 ```yaml
 steps:
diff --git a/src/auth.ts b/src/auth.ts
index c3c25112..473343d3 100644
--- a/src/auth.ts
+++ b/src/auth.ts
@@ -355,12 +355,15 @@ export function parseMavenMirrors(entries: string[]): MavenMirror[] {
 
     const separator = entry.indexOf(':');
     const remainder = entry.slice(separator + 1).trim();
-    // Consume the URL scheme before looking for the selector delimiter. Selector
-    // tokens may themselves contain colons (external:* and external:http:*).
-    const scheme = /^[A-Za-z][A-Za-z0-9+.-]*:/.exec(remainder)?.[0] ?? '';
+    // Protect scheme/authority colons (including IPv6 and ports) before
+    // finding the selector, which may itself contain external:http:*.
+    const urlPrefix =
+      /^[A-Za-z][A-Za-z0-9+.-]*:(?:\/\/(?:[^/?#@\s]*@)?(?:\[[^\]]+\]|[^:/?#\s]+)(?::\d+(?=[/?#:\s]|$))?)?/.exec(
+        remainder
+      )?.[0] ?? '';
     const fields =
       /^(.*?):((?:\s*!?external:(?:http:)?\*\s*|[^:,]*)(?:,(?:\s*!?external:(?:http:)?\*\s*|[^:,]*))*)$/.exec(
-        remainder.slice(scheme.length)
+        remainder.slice(urlPrefix.length)
       );
     if (separator < 0 || !fields) {
       throw new Error(
@@ -369,7 +372,7 @@ export function parseMavenMirrors(entries: string[]): MavenMirror[] {
     }
 
     const id = entry.slice(0, separator).trim();
-    const url = `${scheme}${fields[1]}`.trim();
+    const url = `${urlPrefix}${fields[1]}`.trim();
     const mirrorOf = fields[2].trim();
     if (!id || !url || !mirrorOf) {
       throw new Error(