diff --git a/php/ext/google/protobuf/message.c b/php/ext/google/protobuf/message.c
index 43c3ca295de2..6f4c69e6e8cc 100644
--- a/php/ext/google/protobuf/message.c
+++ b/php/ext/google/protobuf/message.c
@@ -551,14 +551,32 @@ bool Message_InitFromPhp(upb_msg *msg, const upb_msgdef *m, zval *init,
  */
 PHP_METHOD(Message, __construct) {
   Message* intern = (Message*)Z_OBJ_P(getThis());
-  const Descriptor* desc = Descriptor_GetFromClassEntry(Z_OBJCE_P(getThis()));
-  const upb_msgdef *msgdef = desc->msgdef;
+  const Descriptor* desc;
+  zend_class_entry *ce = Z_OBJCE_P(getThis());
   upb_arena *arena = Arena_Get(&intern->arena);
   zval *init_arr = NULL;
 
-  intern->desc = desc;
-  intern->msg = upb_msg_new(msgdef, arena);
-  ObjCache_Add(intern->msg, &intern->std);
+  // This descriptor should always be available, as the generated __construct
+  // method calls initOnce() to load the descriptor prior to calling us.
+  //
+  // However, if the user created their own class derived from Message, this
+  // will trigger an infinite construction loop and blow the stack.  We
+  // temporarily clear create_object to break this loop (see check in
+  // NameMap_GetMessage()).
+  PBPHP_ASSERT(ce->create_object == Message_create);
+  ce->create_object = NULL;
+  desc = Descriptor_GetFromClassEntry(ce);
+  ce->create_object = Message_create;
+
+  if (!desc) {
+    zend_throw_exception_ex(
+        NULL, 0,
+        "Couldn't find descriptor. Note only generated code may derive from "
+        "\\Google\\Protobuf\\Internal\\Message");
+    return;
+  }
+
+  Message_Initialize(intern, desc);
 
   if (zend_parse_parameters(ZEND_NUM_ARGS(), "|a!", &init_arr) == FAILURE) {
     return;
diff --git a/php/src/Google/Protobuf/Internal/Message.php b/php/src/Google/Protobuf/Internal/Message.php
index c02d2b451729..64aadf9d260c 100644
--- a/php/src/Google/Protobuf/Internal/Message.php
+++ b/php/src/Google/Protobuf/Internal/Message.php
@@ -93,8 +93,9 @@ private function initWithGeneratedPool()
         $pool = DescriptorPool::getGeneratedPool();
         $this->desc = $pool->getDescriptorByClassName(get_class($this));
         if (is_null($this->desc)) {
-            user_error(get_class($this) . " is not found in descriptor pool.");
-            return;
+          throw new \InvalidArgumentException(
+            get_class($this) ." is not found in descriptor pool. " .
+            'Only generated classes may derive from Message.');
         }
         foreach ($this->desc->getField() as $field) {
             $setter = $field->getSetter();
diff --git a/php/tests/GeneratedClassTest.php b/php/tests/GeneratedClassTest.php
index 90c1069ed3c6..bf57ead73bc3 100644
--- a/php/tests/GeneratedClassTest.php
+++ b/php/tests/GeneratedClassTest.php
@@ -24,6 +24,13 @@
 use PBEmpty\PBEcho\TestEmptyPackage;
 use Php\Test\TestNamespace;
 
+# This is not allowed, but we at least shouldn't crash.
+class C extends \Google\Protobuf\Internal\Message {
+    public function __construct($data = null) {
+        parent::__construct($data);
+    }
+}
+
 class GeneratedClassTest extends TestBase
 {
 
@@ -1671,6 +1678,33 @@ public function testDeepEquality()
         # TODO: what about unknown fields?
     }
 
+    #########################################################
+    # Test hasOneof<Field> methods exists and working
+    #########################################################
+
+    public function testHasOneof() {
+        $m = new TestMessage();
+        $this->assertFalse($m->hasOneofInt32());
+        $m->setOneofInt32(42);
+        $this->assertTrue($m->hasOneofInt32());
+        $m->setOneofString("bar");
+        $this->assertFalse($m->hasOneofInt32());
+        $this->assertTrue($m->hasOneofString());
+        $m->clear();
+        $this->assertFalse($m->hasOneofInt32());
+        $this->assertFalse($m->hasOneofString());
+    }
+
+    #########################################################
+    # Test that we don't crash if users create their own messages.
+    #########################################################
+
+    public function testUserDefinedClass() {
+      # This is not allowed, but at least we shouldn't crash.
+      $this->expectException(Exception::class);
+      $p = new C();
+    }
+
     #########################################################
     # Test no segfault when error happens
     #########################################################