diff --git a/composer/Composer.php b/composer/Composer.php
index 0a76fc7..6964446 100644
--- a/composer/Composer.php
+++ b/composer/Composer.php
@@ -49,4 +49,15 @@ public static function drupalVersionBranch() {
     return preg_replace('#\.[0-9]+-dev#', '.x-dev', \Drupal::VERSION);
   }
 
+  /**
+   * Return a composer constraint for the current Drupal core minor branch.
+   *
+   * @return string
+   *   A composer constraint for the current minor branch, e.g. '^8.9'or '^9.0'.
+   */
+  public static function drupalVersionConstraint() {
+    [$major, $minor] = explode('.', \Drupal::VERSION);
+    return "^$major.$minor";
+  }
+
 }
diff --git a/composer/Generator/Builder/DrupalDevDependenciesBuilder.php b/composer/Generator/Builder/DrupalDevDependenciesBuilder.php
index b282d23..a098f8f 100644
--- a/composer/Generator/Builder/DrupalDevDependenciesBuilder.php
+++ b/composer/Generator/Builder/DrupalDevDependenciesBuilder.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\Composer\Generator\Builder;
 
+use Drupal\Composer\Composer;
+
 /**
  * Builder to produce metapackage for drupal/core-dev.
  */
@@ -23,6 +25,8 @@ public function getPackage() {
 
     // Put everything from Drupal's "require-dev" into our "require" section.
     $composer['require'] = $this->drupalCoreInfo->getRequireDev();
+    // Depend on the correct branch of drupal/core.
+    $composer['require']['drupal/core'] = Composer::drupalVersionConstraint();
 
     // Sort our required packages by key.
     ksort($composer['require']);