diff --git a/bin/find-composer-packages.php b/bin/find-composer-packages.php
index 4fcef83..a6a71a3 100755
--- a/bin/find-composer-packages.php
+++ b/bin/find-composer-packages.php
@@ -24,6 +24,15 @@
 }
 
 $loader = require($argv[1]);
+$rootComposerFile = realpath(dirname($argv[1]) . '/../composer.json');
+
+if (! file_exists($rootComposerFile)) {
+    fwrite(STDERR, sprintf("ERROR: Unable to find root composer.json file \"%s\"\n", $rootComposerFile));
+    exit(2);
+}
+
+$rootComposerConfig = json_decode(file_get_contents($rootComposerFile), true);
+
 
 // Get length of file path (returned by $loader) up to package dir inside composer
 $needle = 'vendor/composer/../';
@@ -62,9 +71,14 @@ function getPackageForClass(ClassLoader $loader, string $class)
             continue;
         }
         try {
-            $version = \Composer\InstalledVersions::getVersion($package);
+            $depVersion = $rootComposerConfig['require'][$package]
+                ?? $rootComposerConfig['require-dev'][$package]
+                ?? null;
+            if ($depVersion === null) {
+                $version = \Composer\InstalledVersions::getVersion($package);
+                $depVersion = substr($version, 0, strrpos($version, '.'));
+            }
             $done[$package] = true;
-            $depVersion = substr($version, 0, strrpos($version, '.'));
             echo "\"$package\": \"^$depVersion\"\n";
         } catch (OutOfBoundsException $exception) {
             // ignore package