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..ac6d49525 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 ($this->runtime->hasConstant('AF_INET6') || Silencer::call(array($this->runtime, 'invoke'), 'inet_pton', array('::')) !== false) {
             $phpIpv6 = new CompletePackage('php-ipv6', $version, $prettyVersion);
             $phpIpv6->setDescription('The PHP interpreter, with IPv6 support');
             $this->addPackage($phpIpv6);
diff --git a/tests/Composer/Test/Repository/PlatformRepositoryTest.php b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
index d90fcbc73..2da09c1dd 100644
--- a/tests/Composer/Test/Repository/PlatformRepositoryTest.php
+++ b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
@@ -95,8 +95,19 @@ class PlatformRepositoryTest extends TestCase
                 ),
                 array(
                     array('inet_pton', array('::'), ''),
-                )
-            )
+                ),
+            ),
+            array(
+                array(
+                    'PHP_VERSION' => '7.2.31-1+ubuntu16.04.1+deb.sury.org+1',
+                ),
+                array(
+                    'php' => '7.2.31',
+                ),
+                array(
+                    array('inet_pton', array('::'), false),
+                ),
+            ),
         );
     }
 
@@ -133,6 +144,39 @@ class PlatformRepositoryTest extends TestCase
         }
     }
 
+    public function testInetPtonRegression()
+    {
+        $runtime = $this->getMockBuilder('Composer\Platform\Runtime')->getMock();
+
+        $runtime
+            ->expects(self::once())
+            ->method('invoke')
+            ->with('inet_pton', array('::'))
+            ->willReturn(false);
+        $runtime
+            ->method('hasConstant')
+            ->willReturnMap(
+                array(
+                    array('PHP_ZTS', false),
+                    array('AF_INET6', false),
+                )
+            );
+        $runtime
+            ->method('getExtensions')
+            ->willReturn(array());
+        $runtime
+            ->method('getConstant')
+            ->willReturnMap(
+                array(
+                    array('PHP_VERSION', null, '7.0.0'),
+                    array('PHP_DEBUG', null, false),
+                )
+            );
+        $repository = new PlatformRepository(array(), array(), $runtime);
+        $package = $repository->findPackage('php-ipv6', '*');
+        self::assertNull($package);
+    }
+
     public static function getLibraryTestCases()
     {
         return array(