diff --git a/extensions/package-manager/src/Command/CheckForUpdatesHandler.php b/extensions/package-manager/src/Command/CheckForUpdatesHandler.php
index 26f2b949e3..70a8d0d33f 100755
--- a/extensions/package-manager/src/Command/CheckForUpdatesHandler.php
+++ b/extensions/package-manager/src/Command/CheckForUpdatesHandler.php
@@ -100,8 +100,13 @@ public function handle(CheckForUpdates $command)
         $composerJson = $this->composerJson->get();
 
         foreach ($installed as $mainPackageUpdate) {
-            // Skip if not an extension
-            if (! $this->extensions->getExtension(Util::nameToId($mainPackageUpdate['name']))) {
+            $isCore = $mainPackageUpdate['name'] === 'flarum/core';
+
+            // Skip if not an extension. flarum/core is not one, but surfacing a new
+            // major of it is the stated purpose of the first command above, and both
+            // LastUpdateCheck::getNewMajorVersion() and the admin frontend read the
+            // flarum/core entry back out of this list, so it has to survive the loop.
+            if (! $isCore && ! $this->extensions->getExtension(Util::nameToId($mainPackageUpdate['name']))) {
                 continue;
             }
 
diff --git a/extensions/package-manager/src/Composer/ComposerJson.php b/extensions/package-manager/src/Composer/ComposerJson.php
index 528ddcd4ec..8c93266a2d 100644
--- a/extensions/package-manager/src/Composer/ComposerJson.php
+++ b/extensions/package-manager/src/Composer/ComposerJson.php
@@ -56,8 +56,15 @@ public function require(string $packageName, string $version): void
                     continue;
                 }
 
-                // Only extensions can all be set to * versioning.
-                if (! $this->extensions->getExtension(Util::nameToId($packageName))) {
+                // Platform requirements such as `php` or `ext-*` have no vendor
+                // segment, so they cannot be turned into an extension id.
+                if (strpos($p, '/') === false) {
+                    continue;
+                }
+
+                // Only extensions can all be set to * versioning. This has to test the
+                // package being iterated, not the wildcard that was passed in.
+                if (! $this->extensions->getExtension(Util::nameToId($p))) {
                     continue;
                 }