diff --git a/src/Php/FuncCallOptimizer.php b/src/Php/FuncCallOptimizer.php
index ac16f2b6..146acbb9 100644
--- a/src/Php/FuncCallOptimizer.php
+++ b/src/Php/FuncCallOptimizer.php
@@ -17,9 +17,6 @@ trait FuncCallOptimizer
         $getArg = function ($i) use ($expr) {
             return $this->parseIdentifier($expr->args[$i]->value);
         };
-        if ($name === 'strlen' or $name === 'sizeof' or $name === 'count') {
-            return 'php::len(' . $getArg(0) . ')';
-        }
         if (count($expr->args) == 1) {
             switch ($name) {
                 case 'intval':
diff --git a/src/Php/MagicMethodDetector.php b/src/Php/MagicMethodDetector.php
index e8cd4a19..88d3d322 100644
--- a/src/Php/MagicMethodDetector.php
+++ b/src/Php/MagicMethodDetector.php
@@ -19,10 +19,43 @@ trait MagicMethodDetector
             if (count($methodDef->functionDef->argInfoList) != 2) {
                 $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take exactly 2 arguments");
             }
+            if (!$methodDef->functionDef->argInfoList[0]->type or $methodDef->functionDef->argInfoList[0]->type != 'string') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take string as argument");
+            }
         } elseif ($name == '__get') {
             if (count($methodDef->functionDef->argInfoList) != 1) {
                 $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take exactly 1 argument");
             }
+        } elseif ($name == '__toString') {
+            if (!$methodDef->functionDef->returnType or $methodDef->functionDef->returnType != 'string') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must return string");
+            }
+        } elseif ($name == '__serialize') {
+            if (!$methodDef->functionDef->returnType or $methodDef->functionDef->returnType != 'array') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must return array");
+            }
+        } elseif ($name == '__unserialize') {
+            if (count($methodDef->functionDef->argInfoList) != 1) {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take exactly 1 argument");
+            } elseif (!$methodDef->functionDef->argInfoList[0]->type or $methodDef->functionDef->argInfoList[0]->type != 'array') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take array as argument");
+            }
+        } elseif ($name == '__isset' or $name == '__unset' or $name == '__set_state') {
+            if (count($methodDef->functionDef->argInfoList) != 1) {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take exactly 1 argument");
+            }
+            if (!$methodDef->functionDef->argInfoList[0]->type or $methodDef->functionDef->argInfoList[0]->type != 'string') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must take string as argument");
+            }
+            if ($name == '__set_state') {
+                if (!$methodDef->functionDef->returnType or $methodDef->functionDef->returnType != 'array') {
+                    $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must return array");
+                }
+            }
+        } elseif ($name == '__debugInfo') {
+            if (!$methodDef->functionDef->returnType or $methodDef->functionDef->returnType != 'array') {
+                $this->fatalError($v, 'Method ' . $this->class . "::{$name}() must return array");
+            }
         }
     }
 }
diff --git a/tests/aot/to-str.phpt b/tests/aot/to-str.phpt
new file mode 100644
index 00000000..53cac6a4
--- /dev/null
+++ b/tests/aot/to-str.phpt
@@ -0,0 +1,13 @@
+--TEST--
+any
+--FILE--
+<?php
+$s = 12345678;
+var_dump(strlen($s));
+var_dump(strrev($s));
+var_dump(strlen(3.1415926));
+?>
+--EXPECT--
+int(8)
+string(8) "87654321"
+int(18)