diff --git a/src/Composer/Platform/Runtime.php b/src/Composer/Platform/Runtime.php
index 82211ec88..3c77a9250 100644
--- a/src/Composer/Platform/Runtime.php
+++ b/src/Composer/Platform/Runtime.php
@@ -34,6 +34,15 @@ class Runtime
         return constant(ltrim($class.'::'.$constant, ':'));
     }
 
+    /**
+     * @param string $fn
+     * @return bool
+     */
+    public function hasFunction($fn)
+    {
+        return function_exists($fn);
+    }
+
     /**
      * @param callable $callable
      * @param array $arguments
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index 5a8f70627..c72c88f14 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -125,7 +125,7 @@ class PlatformRepository extends ArrayRepository
 
         // The AF_INET6 constant is only defined if ext-sockets is available but
         // IPv6 support might still be available.
-        if ($this->runtime->hasConstant('AF_INET6') || Silencer::call(array($this->runtime, 'invoke'), array('inet_pton', '::')) !== false) {
+        if ($this->runtime->hasConstant('AF_INET6') || ($this->runtime->hasFunction('inet_pton') && Silencer::call(array($this->runtime, 'invoke'), array('inet_pton', '::')) !== false)) {
             $phpIpv6 = new CompletePackage('php-ipv6', $version, $prettyVersion);
             $phpIpv6->setDescription('The PHP interpreter, with IPv6 support');
             $this->addPackage($phpIpv6);