diff --git a/specs/func-declaration/global.php b/specs/func-declaration/global.php
index c74e5805..b196ca87 100644
--- a/specs/func-declaration/global.php
+++ b/specs/func-declaration/global.php
@@ -112,14 +112,36 @@ class Y {}
     use ArrayIterator;
 
     function foo(
-        Foo $arg0,
-        \Foo $arg1,
-        Foo\Bar $arg2,
-        \Foo\Bar $arg3,
-        ArrayIterator $arg4,
-        \ArrayIterator $arg5,
-        X\Y $arg6,
-        \X\Y $arg7
+        string $arg0,
+        ?string $arg1,
+        ?string $arg2 = null,
+        
+        Foo $arg3,
+        ?Foo $arg4,
+        Foo $arg5 = null,
+        
+        \Foo $arg6,
+        ?\Foo $arg7,
+        \Foo $arg8 = null,
+        
+        Foo\Bar $arg9,
+        ?Foo\Bar $arg10,
+        Foo\Bar $arg11 = null,
+        
+        \Foo\Bar $arg7,
+        ?\Foo\Bar $arg12,
+        \Foo\Bar $arg13 = null,
+        
+        ArrayIterator $arg14,
+        ?ArrayIterator $arg15,
+        ?ArrayIterator $arg16 = null,
+        
+        \ArrayIterator $arg17,
+        ?\ArrayIterator $arg18,
+        \ArrayIterator $arg19 = null,
+        
+        X\Y $arg20,
+        \X\Y $arg21
     ) {}
 }
 
@@ -146,7 +168,7 @@ class_alias('Humbug\\X\\Y', 'X\\Y', \false);
 
 use Humbug\Foo;
 use ArrayIterator;
-function foo(\Humbug\Foo $arg0, \Humbug\Foo $arg1, \Humbug\Foo\Bar $arg2, \Humbug\Foo\Bar $arg3, \ArrayIterator $arg4, \ArrayIterator $arg5, \Humbug\X\Y $arg6, \Humbug\X\Y $arg7)
+function foo(string $arg0, ?string $arg1, ?string $arg2 = null, \Humbug\Foo $arg3, ?\Humbug\Foo $arg4, \Humbug\Foo $arg5 = null, \Humbug\Foo $arg6, ?\Humbug\Foo $arg7, \Humbug\Foo $arg8 = null, \Humbug\Foo\Bar $arg9, ?\Humbug\Foo\Bar $arg10, \Humbug\Foo\Bar $arg11 = null, \Humbug\Foo\Bar $arg7, ?\Humbug\Foo\Bar $arg12, \Humbug\Foo\Bar $arg13 = null, \ArrayIterator $arg14, ?\ArrayIterator $arg15, ?\ArrayIterator $arg16 = null, \ArrayIterator $arg17, ?\ArrayIterator $arg18, \ArrayIterator $arg19 = null, \Humbug\X\Y $arg20, \Humbug\X\Y $arg21)
 {
 }
 
@@ -182,7 +204,6 @@ class Y {}
     use ArrayIterator;
     
     function foo(): void {}
-    function foo(): null {}
     
     function foo(): bool {}
     function foo(): ?bool {}
@@ -246,9 +267,6 @@ class_alias('Humbug\\X\\Y', 'X\\Y', \false);
 function foo() : void
 {
 }
-function foo() : null
-{
-}
 function foo() : bool
 {
 }
@@ -291,40 +309,40 @@ function foo() : callable
 function foo() : ?callable
 {
 }
-function foo() : Foo
+function foo() : \Humbug\Foo
 {
 }
-function foo() : \Foo
+function foo() : \Humbug\Foo
 {
 }
-function foo() : ?Foo
+function foo() : ?\Humbug\Foo
 {
 }
-function foo() : ?\Foo
+function foo() : ?\Humbug\Foo
 {
 }
-function foo() : ArrayIterator
+function foo() : \ArrayIterator
 {
 }
 function foo() : \ArrayIterator
 {
 }
-function foo() : ?ArrayIterator
+function foo() : ?\ArrayIterator
 {
 }
 function foo() : ?\ArrayIterator
 {
 }
-function foo() : X\Y
+function foo() : \Humbug\X\Y
 {
 }
-function foo() : \X\Y
+function foo() : \Humbug\X\Y
 {
 }
-function foo() : ?X\Y
+function foo() : ?\Humbug\X\Y
 {
 }
-function foo() : ?\X\Y
+function foo() : ?\Humbug\X\Y
 {
 }
 
diff --git a/specs/func-declaration/method.php b/specs/func-declaration/method.php
new file mode 100644
index 00000000..91663baf
--- /dev/null
+++ b/specs/func-declaration/method.php
@@ -0,0 +1,287 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the humbug/php-scoper package.
+ *
+ * Copyright (c) 2017 Théo FIDRY <theo.fidry@gmail.com>,
+ *                    Pádraic Brady <padraic.brady@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+return [
+    'meta' => [
+        'title' => 'Method declarations',
+        // Default values. If not specified will be the one used
+        'prefix' => 'Humbug',
+        'whitelist' => [],
+    ],
+
+    [
+        'spec' => <<<'SPEC'
+Method declarations:
+- prefix the namespace statements
+- prefix the appropriate classes
+SPEC
+        ,
+        'whitelist' => ['X\Y'],
+        'payload' => <<<'PHP'
+<?php
+
+namespace {
+    class Foo {}
+}
+
+namespace Foo {
+    class Bar {}
+}
+
+namespace X {
+    class Y {}
+}
+
+namespace {
+    class Main {
+        function foo(
+            Foo $arg0,
+            \Foo $arg1,
+            Foo\Bar $arg2,
+            \Foo\Bar $arg3,
+            ArrayIterator $arg4,
+            \ArrayIterator $arg5,
+            X\Y $arg6,
+            \X\Y $arg7
+        ) {}
+
+        static function foo(
+            Foo $arg0,
+            \Foo $arg1,
+            Foo\Bar $arg2,
+            \Foo\Bar $arg3,
+            ArrayIterator $arg4,
+            \ArrayIterator $arg5,
+            X\Y $arg6,
+            \X\Y $arg7
+        ) {}
+    }
+}
+----
+<?php
+
+namespace Humbug;
+
+class Foo
+{
+}
+namespace Humbug\Foo;
+
+class Bar
+{
+}
+namespace Humbug\X;
+
+class Y
+{
+}
+class_alias('Humbug\\X\\Y', 'X\\Y', \false);
+namespace Humbug;
+
+class Main
+{
+    function foo(\Humbug\Foo $arg0, \Humbug\Foo $arg1, \Humbug\Foo\Bar $arg2, \Humbug\Foo\Bar $arg3, \ArrayIterator $arg4, \ArrayIterator $arg5, \Humbug\X\Y $arg6, \Humbug\X\Y $arg7)
+    {
+    }
+    static function foo(\Humbug\Foo $arg0, \Humbug\Foo $arg1, \Humbug\Foo\Bar $arg2, \Humbug\Foo\Bar $arg3, \ArrayIterator $arg4, \ArrayIterator $arg5, \Humbug\X\Y $arg6, \Humbug\X\Y $arg7)
+    {
+    }
+}
+
+PHP
+    ],
+
+    [
+        'spec' => <<<'SPEC'
+Method declarations with return types:
+- prefix namespace statements
+- prefix the appropriate classes
+- append the class_alias statement to the whitelisted class
+SPEC
+        ,
+        'whitelist' => ['X\Y'],
+        'payload' => <<<'PHP'
+<?php
+
+namespace {
+    class Foo {}
+}
+
+namespace Foo {
+    class Bar {}
+}
+
+namespace X {
+    class Y {}
+}
+
+namespace {
+    use Foo;
+    use ArrayIterator;
+    
+    class Main {
+        function foo(): self {}
+        function foo(): void {}
+        
+        function foo(): bool {}
+        function foo(): ?bool {}
+        
+        function foo(): int {}
+        function foo(): ?int {}
+        
+        function foo(): float {}
+        function foo(): ?float {}
+        
+        function foo(): string {}
+        function foo(): ?string {}
+        
+        function foo(): array {}
+        function foo(): ?array {}
+        
+        function foo(): iterable {}
+        function foo(): ?iterable {}
+        
+        function foo(): callable {}
+        function foo(): ?callable {}
+    
+        function foo(): Foo {}
+        function foo(): \Foo {}
+        function foo(): ?Foo {}
+        function foo(): ?\Foo {}
+    
+        function foo(): ArrayIterator {}
+        function foo(): \ArrayIterator {}
+        function foo(): ?ArrayIterator {}
+        function foo(): ?\ArrayIterator {}
+        
+        function foo(): X\Y {}
+        function foo(): \X\Y {}
+        function foo(): ?X\Y {}
+        function foo(): ?\X\Y {}
+    }
+}
+----
+<?php
+
+namespace Humbug;
+
+class Foo
+{
+}
+namespace Humbug\Foo;
+
+class Bar
+{
+}
+namespace Humbug\X;
+
+class Y
+{
+}
+class_alias('Humbug\\X\\Y', 'X\\Y', \false);
+namespace Humbug;
+
+use Humbug\Foo;
+use ArrayIterator;
+class Main
+{
+    function foo() : self
+    {
+    }
+    function foo() : void
+    {
+    }
+    function foo() : bool
+    {
+    }
+    function foo() : ?bool
+    {
+    }
+    function foo() : int
+    {
+    }
+    function foo() : ?int
+    {
+    }
+    function foo() : float
+    {
+    }
+    function foo() : ?float
+    {
+    }
+    function foo() : string
+    {
+    }
+    function foo() : ?string
+    {
+    }
+    function foo() : array
+    {
+    }
+    function foo() : ?array
+    {
+    }
+    function foo() : iterable
+    {
+    }
+    function foo() : ?iterable
+    {
+    }
+    function foo() : callable
+    {
+    }
+    function foo() : ?callable
+    {
+    }
+    function foo() : \Humbug\Foo
+    {
+    }
+    function foo() : \Humbug\Foo
+    {
+    }
+    function foo() : ?\Humbug\Foo
+    {
+    }
+    function foo() : ?\Humbug\Foo
+    {
+    }
+    function foo() : \ArrayIterator
+    {
+    }
+    function foo() : \ArrayIterator
+    {
+    }
+    function foo() : ?\ArrayIterator
+    {
+    }
+    function foo() : ?\ArrayIterator
+    {
+    }
+    function foo() : \Humbug\X\Y
+    {
+    }
+    function foo() : \Humbug\X\Y
+    {
+    }
+    function foo() : ?\Humbug\X\Y
+    {
+    }
+    function foo() : ?\Humbug\X\Y
+    {
+    }
+}
+
+PHP
+    ],
+];
diff --git a/specs/func-declaration/namespace.php b/specs/func-declaration/namespace.php
index d0d36679..cd4be748 100644
--- a/specs/func-declaration/namespace.php
+++ b/specs/func-declaration/namespace.php
@@ -56,7 +56,7 @@ class Foo {}
     class ArrayIterator {}
 
     function foo(
-        Foo $arg0,
+        Foo $arg0 = null,
         \Foo $arg1,
         Foo\Bar $arg2,
         \Foo\Bar $arg3,
@@ -103,7 +103,7 @@ class Foo
 class ArrayIterator
 {
 }
-function foo(\Humbug\Pi\Foo $arg0, \Humbug\Foo $arg1, \Humbug\Pi\Foo\Bar $arg2, \Humbug\Foo\Bar $arg3, \Humbug\Pi\ArrayIterator $arg4, \ArrayIterator $arg5, \Humbug\Pi\X\Y $arg6, \Humbug\X\Y $arg7)
+function foo(\Humbug\Pi\Foo $arg0 = null, \Humbug\Foo $arg1, \Humbug\Pi\Foo\Bar $arg2, \Humbug\Foo\Bar $arg3, \Humbug\Pi\ArrayIterator $arg4, \ArrayIterator $arg5, \Humbug\Pi\X\Y $arg6, \Humbug\X\Y $arg7)
 {
 }
 
@@ -223,7 +223,6 @@ class Y {}
     use ArrayIterator;
     
     function foo(): void {}
-    function foo(): null {}
     
     function foo(): bool {}
     function foo(): ?bool {}
@@ -287,9 +286,6 @@ class_alias('Humbug\\X\\Y', 'X\\Y', \false);
 function foo() : void
 {
 }
-function foo() : null
-{
-}
 function foo() : bool
 {
 }
@@ -332,40 +328,40 @@ function foo() : callable
 function foo() : ?callable
 {
 }
-function foo() : Foo
+function foo() : \Humbug\Foo
 {
 }
-function foo() : \Foo
+function foo() : \Humbug\Foo
 {
 }
-function foo() : ?Foo
+function foo() : ?\Humbug\Foo
 {
 }
-function foo() : ?\Foo
+function foo() : ?\Humbug\Foo
 {
 }
-function foo() : ArrayIterator
+function foo() : \ArrayIterator
 {
 }
 function foo() : \ArrayIterator
 {
 }
-function foo() : ?ArrayIterator
+function foo() : ?\ArrayIterator
 {
 }
 function foo() : ?\ArrayIterator
 {
 }
-function foo() : X\Y
+function foo() : \Humbug\Pi\X\Y
 {
 }
-function foo() : \X\Y
+function foo() : \Humbug\X\Y
 {
 }
-function foo() : ?X\Y
+function foo() : ?\Humbug\Pi\X\Y
 {
 }
-function foo() : ?\X\Y
+function foo() : ?\Humbug\X\Y
 {
 }
 
diff --git a/src/NodeVisitor/NameStmtPrefixer.php b/src/NodeVisitor/NameStmtPrefixer.php
index 9c91ec14..211801db 100644
--- a/src/NodeVisitor/NameStmtPrefixer.php
+++ b/src/NodeVisitor/NameStmtPrefixer.php
@@ -24,8 +24,11 @@
 use PhpParser\Node\Expr\StaticCall;
 use PhpParser\Node\Name;
 use PhpParser\Node\Name\FullyQualified;
+use PhpParser\Node\NullableType;
 use PhpParser\Node\Param;
 use PhpParser\Node\Stmt\Class_;
+use PhpParser\Node\Stmt\ClassMethod;
+use PhpParser\Node\Stmt\Function_;
 use PhpParser\Node\Stmt\Interface_;
 use PhpParser\NodeVisitorAbstract;
 
@@ -44,7 +47,7 @@
  */
 final class NameStmtPrefixer extends NodeVisitorAbstract
 {
-    private const PHP_FUNCTION_KEYWORDS = [
+    public const PHP_FUNCTION_KEYWORDS = [
         'self',
         'static',
         'parent',
@@ -84,12 +87,22 @@ private function prefixName(Name $name): Node
     {
         $parentNode = AppendParentNode::getParent($name);
 
+        if ($parentNode instanceof NullableType) {
+            if (false === AppendParentNode::hasParent($parentNode)) {
+                return $name;
+            }
+
+            $parentNode = AppendParentNode::getParent($parentNode);
+        }
+
         if (false === (
                 $parentNode instanceof ConstFetch
                 || $parentNode instanceof ClassConstFetch
                 || $parentNode instanceof Param
                 || $parentNode instanceof FuncCall
                 || $parentNode instanceof StaticCall
+                || $parentNode instanceof Function_
+                || $parentNode instanceof ClassMethod
                 || $parentNode instanceof New_
                 || $parentNode instanceof Class_
                 || $parentNode instanceof Interface_
@@ -106,11 +119,15 @@ private function prefixName(Name $name): Node
                 || $parentNode instanceof New_
                 || $parentNode instanceof Param
             )
-            && in_array((string) $name, self::PHP_FUNCTION_KEYWORDS)
+            && in_array((string) $name, self::PHP_FUNCTION_KEYWORDS, true)
         ) {
             return $name;
         }
 
+        if ($parentNode instanceof ConstFetch && 'null' === (string) $name) {
+            return $name;
+        }
+
         $resolvedValue = $this->nameResolver->resolveName($name);
 
         $resolvedName = $resolvedValue->getName();
@@ -150,6 +167,10 @@ private function prefixName(Name $name): Node
             return $resolvedName;
         }
 
+        if ('self' === (string) $resolvedName && $parentNode instanceof ClassMethod) {
+            return $name;
+        }
+
         return FullyQualified::concat(
             $this->prefix,
             $resolvedName->toString(),
diff --git a/src/NodeVisitor/Resolver/FullyQualifiedNameResolver.php b/src/NodeVisitor/Resolver/FullyQualifiedNameResolver.php
index a676eafd..2394895f 100644
--- a/src/NodeVisitor/Resolver/FullyQualifiedNameResolver.php
+++ b/src/NodeVisitor/Resolver/FullyQualifiedNameResolver.php
@@ -17,10 +17,12 @@
 use Humbug\PhpScoper\NodeVisitor\AppendParentNode;
 use Humbug\PhpScoper\NodeVisitor\Collection\NamespaceStmtCollection;
 use Humbug\PhpScoper\NodeVisitor\Collection\UseStmtCollection;
+use Humbug\PhpScoper\NodeVisitor\NameStmtPrefixer;
 use PhpParser\Node\Expr\ConstFetch;
 use PhpParser\Node\Expr\FuncCall;
 use PhpParser\Node\Name;
 use PhpParser\Node\Name\FullyQualified;
+use function in_array;
 
 /**
  * Attempts to resolve the node name into a fully qualified node. Returns a valid (non fully-qualified) name node on
@@ -64,6 +66,10 @@ private function resolveNodeName(Name $name, ?Name $namespace, ?Name $use): Name
             return new FullyQualified($name, $name->getAttributes());
         }
 
+        if (in_array((string) $name, NameStmtPrefixer::PHP_FUNCTION_KEYWORDS, true)) {
+            return $name;
+        }
+
         $parentNode = AppendParentNode::getParent($name);
 
         if (