diff --git a/NEWS b/NEWS
index cb27125a7e1..c03d6879330 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,8 @@ PHP                                                                        NEWS
     (nielsdos)
   . Fixed bug GH-17101 (AST->string does not reproduce constructor property
     promotion correctly). (nielsdos)
+  . Fixed bug GH-17211 (observer segfault on function loaded with dl()).
+    (Arnaud)
 
 - Date:
   . Fixed bug GH-14709 DatePeriod::__construct() overflow on recurrences.
diff --git a/Zend/zend_API.c b/Zend/zend_API.c
index e93c4a93b7d..13c640a64dd 100644
--- a/Zend/zend_API.c
+++ b/Zend/zend_API.c
@@ -2817,7 +2817,14 @@ ZEND_API zend_result zend_register_functions(zend_class_entry *scope, const zend
 	}
 	internal_function->type = ZEND_INTERNAL_FUNCTION;
 	internal_function->module = EG(current_module);
-	internal_function->T = 0;
+	if (EG(active) && ZEND_OBSERVER_ENABLED) {
+		/* Add an observer temporary to store previous observed frames. This is
+		 * normally handled by zend_observer_post_startup(), except for
+		 * functions registered at runtime (EG(active)). */
+		internal_function->T = 1;
+	} else {
+		internal_function->T = 0;
+	}
 	memset(internal_function->reserved, 0, ZEND_MAX_RESERVED_RESOURCES * sizeof(void*));
 
 	while (ptr->fname) {
diff --git a/ext/dl_test/dl_test.c b/ext/dl_test/dl_test.c
index 5a5dfee33f5..1121a96b9df 100644
--- a/ext/dl_test/dl_test.c
+++ b/ext/dl_test/dl_test.c
@@ -76,9 +76,27 @@ PHP_INI_BEGIN()
 PHP_INI_END()
 /* }}} */
 
+PHP_METHOD(DlTest, test)
+{
+	char *var = "World";
+	size_t var_len = sizeof("World") - 1;
+	zend_string *retval;
+
+	ZEND_PARSE_PARAMETERS_START(0, 1)
+		Z_PARAM_OPTIONAL
+		Z_PARAM_STRING(var, var_len)
+	ZEND_PARSE_PARAMETERS_END();
+
+	retval = strpprintf(0, "Hello %s", var);
+
+	RETURN_STR(retval);
+}
+
 /* {{{ PHP_MINIT_FUNCTION */
 PHP_MINIT_FUNCTION(dl_test)
 {
+	register_class_DlTest();
+
 	/* Test backwards compatibility */
 	if (getenv("PHP_DL_TEST_USE_OLD_REGISTER_INI_ENTRIES")) {
 		zend_register_ini_entries(ini_entries, module_number);
diff --git a/ext/dl_test/dl_test.stub.php b/ext/dl_test/dl_test.stub.php
index 524c8206365..cd8b3916bae 100644
--- a/ext/dl_test/dl_test.stub.php
+++ b/ext/dl_test/dl_test.stub.php
@@ -8,3 +8,7 @@
 function dl_test_test1(): void {}
 
 function dl_test_test2(string $str = ""): string {}
+
+class DlTest {
+    public function test(string $str = ""): string {}
+}
diff --git a/ext/dl_test/dl_test_arginfo.h b/ext/dl_test/dl_test_arginfo.h
index fdd0e3a89e1..0618bbdb222 100644
--- a/ext/dl_test/dl_test_arginfo.h
+++ b/ext/dl_test/dl_test_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 547ddbc21e9aa853b491cb17e902bbbb9cc2df00 */
+ * Stub hash: 2dbacf5282b0f8e53923ac70495c2da43c7237e3 */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_dl_test_test1, 0, 0, IS_VOID, 0)
 ZEND_END_ARG_INFO()
@@ -8,9 +8,12 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_dl_test_test2, 0, 0, IS_STRING,
 	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, str, IS_STRING, 0, "\"\"")
 ZEND_END_ARG_INFO()
 
+#define arginfo_class_DlTest_test arginfo_dl_test_test2
+
 
 ZEND_FUNCTION(dl_test_test1);
 ZEND_FUNCTION(dl_test_test2);
+ZEND_METHOD(DlTest, test);
 
 
 static const zend_function_entry ext_functions[] = {
@@ -18,3 +21,19 @@ static const zend_function_entry ext_functions[] = {
 	ZEND_FE(dl_test_test2, arginfo_dl_test_test2)
 	ZEND_FE_END
 };
+
+
+static const zend_function_entry class_DlTest_methods[] = {
+	ZEND_ME(DlTest, test, arginfo_class_DlTest_test, ZEND_ACC_PUBLIC)
+	ZEND_FE_END
+};
+
+static zend_class_entry *register_class_DlTest(void)
+{
+	zend_class_entry ce, *class_entry;
+
+	INIT_CLASS_ENTRY(ce, "DlTest", class_DlTest_methods);
+	class_entry = zend_register_internal_class_ex(&ce, NULL);
+
+	return class_entry;
+}
diff --git a/ext/standard/tests/general_functions/gh17211.phpt b/ext/standard/tests/general_functions/gh17211.phpt
new file mode 100644
index 00000000000..5df8a6638a6
--- /dev/null
+++ b/ext/standard/tests/general_functions/gh17211.phpt
@@ -0,0 +1,42 @@
+--TEST--
+dl() / observer segfault
+--EXTENSIONS--
+zend_test
+--SKIPIF--
+<?php include dirname(__DIR__, 3) . "/dl_test/tests/skip.inc"; ?>
+--INI--
+zend_test.observer.enabled=1
+zend_test.observer.observe_functions=1
+zend_test.observer.show_output=1
+--FILE--
+<?php
+
+if (PHP_OS_FAMILY === 'Windows') {
+    $loaded = dl('php_dl_test.dll');
+} else {
+    $loaded = dl('dl_test.so');
+}
+
+var_dump(dl_test_test2("World!"));
+
+$test = new DlTest();
+var_dump($test->test("World!"));
+?>
+--EXPECTF--
+<!-- init '%sgh17211.php' -->
+<!-- init dl() -->
+<dl>
+</dl>
+<!-- init dl_test_test2() -->
+<dl_test_test2>
+</dl_test_test2>
+<!-- init var_dump() -->
+<var_dump>
+string(12) "Hello World!"
+</var_dump>
+<!-- init DlTest::test() -->
+<DlTest::test>
+</DlTest::test>
+<var_dump>
+string(12) "Hello World!"
+</var_dump>