diff --git a/phpunit/src/Generator/UtilsTest.php b/phpunit/src/Generator/UtilsTest.php
index b94a0468..bcab4f74 100644
--- a/phpunit/src/Generator/UtilsTest.php
+++ b/phpunit/src/Generator/UtilsTest.php
@@ -186,6 +186,13 @@ class UtilsTest extends TestCase
         $this->assertStringStartsWith('_php__var__', $result);
     }
 
+    public function testEscapeVarNameStdioMacros(): void
+    {
+        foreach (['stdin', 'stdout', 'stderr'] as $name) {
+            $this->assertEquals('_php__var__' . $name, $this->invokeMethod('escapeVarName', $name));
+        }
+    }
+
     public function testUnescapeVarName(): void
     {
         $this->assertEquals('foo', $this->invokeMethod('unescapeVarName', '_php__var__foo'));
diff --git a/src/Metadata/Constants.php b/src/Metadata/Constants.php
index 019fc076..6c61b97f 100644
--- a/src/Metadata/Constants.php
+++ b/src/Metadata/Constants.php
@@ -109,6 +109,9 @@ class Constants
         'while',
         'xor',
         'xor_eq',
+        'stdin',  // C stdio macros
+        'stdout',
+        'stderr',
         'pipe',
         'errno', // Linux error code
         'this_', // phpx keywords