diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index <HASH>..<HASH> 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -20,6 +20,7 @@ use Composer\Factory;
 use Composer\Installer;
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
+use Composer\Package\Version\VersionParser;
 
 /**
  * @author Jérémy Romey <jeremy@free-agent.fr>
@@ -80,6 +81,12 @@ EOT
         $baseRequirements = array_key_exists($requireKey, $composer) ? $composer[$requireKey] : array();
         $requirements = $this->formatRequirements($requirements);
 
+        // validate requirements format
+        $versionParser = new VersionParser();
+        foreach ($requirements as $constraint) {
+            $versionParser->parseConstraints($constraint);
+        }
+
         if (!$this->updateFileCleanly($json, $baseRequirements, $requirements, $requireKey)) {
             foreach ($requirements as $package => $version) {
                 $baseRequirements[$package] = $version;
Validate constraints in require command, fixes #<I>