diff --git a/src/TypeSystem/CompositeTypeCheckerTrait.php b/src/TypeSystem/CompositeTypeCheckerTrait.php
index 8ce63cdd..77762b4d 100644
--- a/src/TypeSystem/CompositeTypeCheckerTrait.php
+++ b/src/TypeSystem/CompositeTypeCheckerTrait.php
@@ -35,7 +35,11 @@ trait CompositeTypeCheckerTrait
         // TYPE_VAR means that the expression is dynamic or its result cannot
         // be represented by the current scalar type system. It must retain the
         // runtime type check.
-        if ($this->detectTypeOfExpr($value) === Type::VAR && !$this->isNullExpr($value)) {
+        // A reference (TYPE_REF) is a Variant reference whose concrete type is
+        // only known at runtime (e.g. an undefined variable auto-created by a
+        // by-reference argument), so it is treated the same way.
+        $valueType = $this->detectTypeOfExpr($value);
+        if (($valueType === Type::VAR || $valueType === Type::REF) && !$this->isNullExpr($value)) {
             return self::COMPOSITE_TYPE_UNKNOWN;
         }
 
diff --git a/tests/compiler/static/static-call-byref-undefined-var.phpt b/tests/compiler/static/static-call-byref-undefined-var.phpt
new file mode 100644
index 00000000..e51f81d5
--- /dev/null
+++ b/tests/compiler/static/static-call-byref-undefined-var.phpt
@@ -0,0 +1,38 @@
+--TEST--
+Static method call passing an undefined variable by reference (late static binding)
+--FILE--
+<?php
+
+class Test
+{
+    public static function getName(?string &$name)
+    {
+        $name = 'test';
+    }
+
+    public static function run()
+    {
+        // $fileName is undefined; passing it by reference must auto-create it
+        // instead of raising an "Undefined variable" fatal error.
+        static::getName($fileName);
+        var_dump($fileName);
+        Test2::dump($fileName);
+    }
+}
+
+class Test2
+{
+    public static function dump(?string $value)
+    {
+        var_dump($value);
+    }
+}
+
+function main()
+{
+    Test::run();
+}
+?>
+--EXPECT--
+string(4) "test"
+string(4) "test"