diff --git a/README.md b/README.md
index 2b56466..cb6bdc6 100644
--- a/README.md
+++ b/README.md
@@ -52,9 +52,10 @@ opcache.enable_cli=1
 ffi.enable="true"
 
 ; List of headers files to preload, wildcard patterns allowed. `ffi.preload` has no effect on Windows.
-; see headers directory `your-php-version`
-;ffi.preload=path/to/vendor/symplely/zend-ffi/headers/ze(your-php-version)_generated.h
+; See headers directory for `your-php-version`, this feature is untested, since not enabled for Windows.
+;ffi.preload=path/to/vendor/symplely/zend-ffi/headers/ze(your-php-version).h
 
+;This feature is untested.
 ;opcache.preload==path/to/vendor/symplely/zend-ffi/preload.php
 ```
 
diff --git a/preload.php b/preload.php
index eb8769a..6645220 100644
--- a/preload.php
+++ b/preload.php
@@ -357,17 +357,26 @@ function is_cdata($ptr): bool
   }
 
   /**
-   * Checks whether the given object is `FFI\CData`, and has the given `field`.
+   * Checks whether the given _c struct_ object is `FFI\CData`, and has the given member `field`.
    *
    * @param object $ptr
-   * @param string $field
+   * @param string $field member depth, up three levels *c_field0->c_field1->c_field2*
    * @return boolean
    */
-  function is_cdata_valid(object $ptr, string $field)
+  function is_cdata_valid(object $ptr, string $field): bool
   {
     try {
-      $isValid = \ffi_object($ptr)->{$field};
-      return \is_null($isValid) || !\is_null($isValid);
+      if (\strpos($field, '->') !== false) {
+        $fields = \explode('->', $field);
+        if (\count($fields) == 3)
+          \ffi_object($ptr)->{$fields[0]}->{$fields[1]}->{$fields[2]};
+        elseif (\count($fields) == 2)
+          \ffi_object($ptr)->{$fields[0]}->{$fields[1]};
+      } else {
+        \ffi_object($ptr)->{$field};
+      }
+
+      return true;
     } catch (\Throwable $e) {
       return false;
     }
@@ -639,7 +648,7 @@ function zend_preloader(): void
     if (\IS_WINDOWS) {
       $mmap_header = __DIR__ . '\\headers\\windows_mman.h';
       if (\file_exists('vendor\\symplely\\zend-ffi')) {
-        $vendor_code = \str_replace('.h', '_vendor.h', $mmap_header);
+        $vendor_code = \str_replace('.h', '_generated.h', $mmap_header);
         if (!\file_exists($vendor_code)) {
           $file = \str_replace(
             'FFI_LIB ".',
diff --git a/tests/900-misc_general_c.phpt b/tests/900-misc_general_c.phpt
index 190fcf5..a0b6f85 100644
--- a/tests/900-misc_general_c.phpt
+++ b/tests/900-misc_general_c.phpt
@@ -25,6 +25,9 @@ $cs = c_struct_type('_php_socket', 'ze', [
     'std' => ZendObject::init($ci)()[0]
 ]);
 var_dump(is_cdata_valid($cs, 'blocking'));
+var_dump(is_cdata_valid($cs, 'block'));
+var_dump(is_cdata_valid($cs, 'zstream->value'));
+var_dump(is_cdata_valid($cs, 'zstream->value->lval'));
 var_dump($cs->sizeof());
 var_dump($cs->alignof());
 var_dump($cs->char());
@@ -57,6 +60,9 @@ object(CStruct)#%d (2) {
   int(1477705728)
 }
 bool(true)
+bool(false)
+bool(true)
+bool(true)
 int(88)
 int(8)
 object(FFI\CData:char*)#%d (1) {