diff --git a/ext/reflection/php_reflection.c b/ext/reflection/php_reflection.c
index e74b7fcb27a7..e560077502ef 100644
--- a/ext/reflection/php_reflection.c
+++ b/ext/reflection/php_reflection.c
@@ -6762,8 +6762,7 @@ ZEND_METHOD(ReflectionProperty, isReadable)
 		RETURN_FALSE;
 	}
 
-	if (prop->flags & ZEND_ACC_VIRTUAL) {
-		ZEND_ASSERT(prop->hooks);
+	if ((prop->flags & ZEND_ACC_VIRTUAL) && prop->hooks) {
 		if (!prop->hooks[ZEND_PROPERTY_HOOK_GET]) {
 			RETURN_FALSE;
 		}
@@ -6854,25 +6853,30 @@ ZEND_METHOD(ReflectionProperty, isWritable)
 		RETURN_FALSE;
 	}
 
-	if (prop->flags & ZEND_ACC_VIRTUAL) {
-		ZEND_ASSERT(prop->hooks);
+	if ((prop->flags & ZEND_ACC_VIRTUAL) && prop->hooks) {
 		if (!prop->hooks[ZEND_PROPERTY_HOOK_SET]) {
 			RETURN_FALSE;
 		}
-	} else if (obj && (prop->flags & ZEND_ACC_READONLY)) {
+	} else if (prop->flags & ZEND_ACC_VIRTUAL) {
+		if (prop->flags & ZEND_ACC_READONLY) {
+			RETURN_FALSE;
+		}
+	} else if ((prop->flags & ZEND_ACC_READONLY)) {
+		if (obj) {
 retry:;
-		zval *prop_val = OBJ_PROP(obj, prop->offset);
-		if (Z_TYPE_P(prop_val) == IS_UNDEF
-		 && zend_lazy_object_must_init(obj)
-		 && (Z_PROP_FLAG_P(prop_val) & IS_PROP_LAZY)) {
-			obj = zend_lazy_object_init(obj);
-			if (!obj) {
-				RETURN_THROWS();
+			zval *prop_val = OBJ_PROP(obj, prop->offset);
+			if (Z_TYPE_P(prop_val) == IS_UNDEF
+		 	&& zend_lazy_object_must_init(obj)
+		 	&& (Z_PROP_FLAG_P(prop_val) & IS_PROP_LAZY)) {
+				obj = zend_lazy_object_init(obj);
+				if (!obj) {
+					RETURN_THROWS();
+				}
+				goto retry;
+			}
+			if (Z_TYPE_P(prop_val) != IS_UNDEF && !(Z_PROP_FLAG_P(prop_val) & IS_PROP_REINITABLE)) {
+				RETURN_FALSE;
 			}
-			goto retry;
-		}
-		if (Z_TYPE_P(prop_val) != IS_UNDEF && !(Z_PROP_FLAG_P(prop_val) & IS_PROP_REINITABLE)) {
-			RETURN_FALSE;
 		}
 	}
 
diff --git a/ext/reflection/tests/gh21768.phpt b/ext/reflection/tests/gh21768.phpt
new file mode 100644
index 000000000000..422239120dbe
--- /dev/null
+++ b/ext/reflection/tests/gh21768.phpt
@@ -0,0 +1,21 @@
+--TEST--
+GH-21768: Assertion failure in ReflectionProperty::is{Readable,Writable}() on internal virtual properties
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+$rc = new ReflectionClass('DOMDocument');
+foreach ($rc->getProperties() as $rp) {
+    if (!$rp->isVirtual())
+	    continue;
+    if (!$rp->isReadable(null))
+	    die("$rp should be readable");
+    if (!$rp->isWritable(null))
+	    die("$rp should be writable");
+}
+echo "done\n";
+
+?>
+--EXPECT--
+done