diff --git a/src/Handler.php b/src/Handler.php
index 20bc10019639b05d8ae1affb3bc0ebeb83ad3ae5..431dc66043a831a469c1d3b7528ddccc70d6a2f6 100644
--- a/src/Handler.php
+++ b/src/Handler.php
@@ -85,6 +85,10 @@ class Handler {
     $installationManager = $this->composer->getInstallationManager();
 
     $drupalCorePackage = $this->getDrupalCorePackage();
+    if (!$drupalCorePackage) {
+      // We are called too early, Drupal core is not available yet.
+      return;
+    }
     $corePath = $installationManager->getInstallPath($drupalCorePackage);
 
     // Directory where the root project is being created