diff --git a/src/Composer/Advisory/Auditor.php b/src/Composer/Advisory/Auditor.php
index 7d55be5dc..00ac610e6 100644
--- a/src/Composer/Advisory/Auditor.php
+++ b/src/Composer/Advisory/Auditor.php
@@ -86,7 +86,10 @@ class Auditor
             if ($ignoredAdvisories !== []) {
                 $json['ignored-advisories'] = $ignoredAdvisories;
             }
-            $json['abandoned'] = $abandonedPackages;
+            $json['abandoned'] = array_reduce($abandonedPackages, static function(array $carry, CompletePackageInterface $package): array {
+                $carry[$package->getPrettyName()] = $package->getReplacementPackage();
+                return $carry;
+            }, []);
 
             $io->write(JsonFile::encode($json));
 
@@ -127,11 +130,11 @@ class Auditor
 
     /**
      * @param array<PackageInterface> $packages
-     * @return array<PackageInterface>
+     * @return array<CompletePackageInterface>
      */
     private function filterAbandonedPackages(array $packages): array
     {
-        return array_filter($packages, function (PackageInterface $pkg) {
+        return array_filter($packages, static function (PackageInterface $pkg) {
             return $pkg instanceof CompletePackageInterface && $pkg->isAbandoned();
         });
     }
@@ -305,7 +308,7 @@ class Auditor
     }
 
     /**
-     * @param array<PackageInterface> $packages
+     * @param array<CompletePackageInterface> $packages
      * @param self::FORMAT_PLAIN|self::FORMAT_TABLE $format
      */
     private function outputAbandonedPackages(IOInterface $io, array $packages, string $format): void
@@ -314,10 +317,6 @@ class Auditor
 
         if ($format === self::FORMAT_PLAIN) {
             foreach ($packages as $pkg) {
-                if (!$pkg instanceof CompletePackageInterface) {
-                    continue;
-                }
-
                 $replacement = $pkg->getReplacementPackage() !== null
                     ? 'Use '.$pkg->getReplacementPackage().' instead'
                     : 'No replacement was suggested';
@@ -341,10 +340,6 @@ class Auditor
             ->setColumnMaxWidth(1, 80);
 
         foreach ($packages as $pkg) {
-            if (!$pkg instanceof CompletePackageInterface) {
-                continue;
-            }
-
             $replacement = $pkg->getReplacementPackage() !== null ? $pkg->getReplacementPackage() : 'none';
             $table->addRow([$this->getPackageNameWithLink($pkg), $replacement]);
         }
diff --git a/tests/Composer/Test/Advisory/AuditorTest.php b/tests/Composer/Test/Advisory/AuditorTest.php
index e42c95e68..656505844 100644
--- a/tests/Composer/Test/Advisory/AuditorTest.php
+++ b/tests/Composer/Test/Advisory/AuditorTest.php
@@ -122,6 +122,26 @@ Found 2 abandoned packages:
 | vendor/abandoned2 | none                                                                             |
 +-------------------+----------------------------------------------------------------------------------+',
         ];
+
+        yield 'abandoned packages fails with json format' => [
+            'data' => [
+                'packages' => [
+                    $abandonedWithReplacement,
+                    $abandonedNoReplacement,
+                ],
+                'warningOnly' => false,
+                'abandoned' => Auditor::ABANDONED_FAIL,
+                'format' => Auditor::FORMAT_JSON,
+            ],
+            'expected' => 2,
+            'output' => '{
+    "advisories": [],
+    "abandoned": {
+        "vendor/abandoned": "foo/bar",
+        "vendor/abandoned2": null
+    }
+}',
+        ];
     }
 
     /**