diff --git a/admin/metabox.php b/admin/metabox.php
index 3772561..e3a7b6c 100644
--- a/admin/metabox.php
+++ b/admin/metabox.php
@@ -114,7 +114,16 @@ function projects_portfolio_save_meta_box( $post_id ) {
         // Maintain the legacy key for backward-compat reads (only when this is a GitHub project).
         $provider_now = get_post_meta( $post_id, '_projects_portfolio_provider', true );
         if ( 'github' === $provider_now ) {
-            update_post_meta( $post_id, '_projects_portfolio_github_url', $repo_url );
+            if ( '' === $repo_url ) {
+                // Clearing the field on a GitHub project should clear the legacy key too.
+                delete_post_meta( $post_id, '_projects_portfolio_github_url' );
+            } else {
+                update_post_meta( $post_id, '_projects_portfolio_github_url', $repo_url );
+            }
+        } else {
+            // Provider is gitea (or any non-github): ensure no stale GitHub URL can
+            // resurrect via the legacy fallback chain.
+            delete_post_meta( $post_id, '_projects_portfolio_github_url' );
         }
     }
 
diff --git a/tests/test-metabox.php b/tests/test-metabox.php
index 348b666..eb88532 100644
--- a/tests/test-metabox.php
+++ b/tests/test-metabox.php
@@ -70,4 +70,76 @@ class Metabox_Test extends \PHPUnit\Framework\TestCase {
         $this->assertSame( 'github', $existing['_projects_portfolio_provider'] );
         $this->assertSame( 'https://github.com/owner/repo', $existing['_projects_portfolio_repo_url'] );
     }
+
+    public function test_switching_to_gitea_deletes_legacy_github_url(): void {
+        $existing = [
+            '_projects_portfolio_provider'  => 'github',
+            '_projects_portfolio_repo_url'  => 'https://github.com/owner/repo',
+            '_projects_portfolio_github_url' => 'https://github.com/owner/repo',
+        ];
+        $deleted = [];
+        \Brain\Monkey\Functions\stubs( [
+            'get_post_meta' => function ( $post_id, $key, $single = false ) use ( &$existing ) {
+                return $existing[ $key ] ?? '';
+            },
+            'update_post_meta' => function ( $post_id, $key, $value ) use ( &$existing ) {
+                $existing[ $key ] = $value;
+                return true;
+            },
+            'delete_post_meta' => function ( $post_id, $key ) use ( &$existing, &$deleted ) {
+                unset( $existing[ $key ] );
+                $deleted[] = $key;
+                return true;
+            },
+            'wp_verify_nonce' => function () { return true; },
+            'wp_nonce_field' => function () { /* noop */ },
+        ] );
+
+        $_POST['projects_portfolio_meta_box_nonce'] = 'nonce';
+        $_POST['projects_portfolio_provider']       = 'gitea';
+        $_POST['projects_portfolio_repo_url']       = 'https://codeberg.org/owner/repo';
+
+        projects_portfolio_save_meta_box( 7 );
+
+        $this->assertSame( 'gitea', $existing['_projects_portfolio_provider'] );
+        $this->assertSame( 'https://codeberg.org/owner/repo', $existing['_projects_portfolio_repo_url'] );
+        $this->assertArrayNotHasKey( '_projects_portfolio_github_url', $existing );
+        $this->assertContains( '_projects_portfolio_github_url', $deleted );
+    }
+
+    public function test_github_with_empty_repo_url_deletes_legacy_github_url(): void {
+        $existing = [
+            '_projects_portfolio_provider'  => 'github',
+            '_projects_portfolio_repo_url'  => 'https://github.com/owner/repo',
+            '_projects_portfolio_github_url' => 'https://github.com/owner/repo',
+        ];
+        $deleted = [];
+        \Brain\Monkey\Functions\stubs( [
+            'get_post_meta' => function ( $post_id, $key, $single = false ) use ( &$existing ) {
+                return $existing[ $key ] ?? '';
+            },
+            'update_post_meta' => function ( $post_id, $key, $value ) use ( &$existing ) {
+                $existing[ $key ] = $value;
+                return true;
+            },
+            'delete_post_meta' => function ( $post_id, $key ) use ( &$existing, &$deleted ) {
+                unset( $existing[ $key ] );
+                $deleted[] = $key;
+                return true;
+            },
+            'wp_verify_nonce' => function () { return true; },
+            'wp_nonce_field' => function () { /* noop */ },
+        ] );
+
+        $_POST['projects_portfolio_meta_box_nonce'] = 'nonce';
+        $_POST['projects_portfolio_provider']       = 'github';
+        $_POST['projects_portfolio_repo_url']       = '';
+
+        projects_portfolio_save_meta_box( 9 );
+
+        $this->assertSame( 'github', $existing['_projects_portfolio_provider'] );
+        $this->assertSame( '', $existing['_projects_portfolio_repo_url'] );
+        $this->assertArrayNotHasKey( '_projects_portfolio_github_url', $existing );
+        $this->assertContains( '_projects_portfolio_github_url', $deleted );
+    }
 }
diff --git a/tests/wp-stubs.php b/tests/wp-stubs.php
index 9d4bb35..6bc1544 100644
--- a/tests/wp-stubs.php
+++ b/tests/wp-stubs.php
@@ -71,6 +71,9 @@ if ( ! function_exists( 'get_post_meta' ) ) {
 if ( ! function_exists( 'update_post_meta' ) ) {
     function update_post_meta( $post_id, $key, $value ) { return true; }
 }
+if ( ! function_exists( 'delete_post_meta' ) ) {
+    function delete_post_meta( $post_id, $key ) { return true; }
+}
 if ( ! function_exists( 'wp_unslash' ) ) {
     function wp_unslash( $value ) { return $value; }
 }