diff --git a/Zend/tests/gh11821.phpt b/Zend/tests/gh11821.phpt
new file mode 100644
index 000000000000..4e34dbe2b4d5
--- /dev/null
+++ b/Zend/tests/gh11821.phpt
@@ -0,0 +1,16 @@
+--TEST--
+GH-11821: Exit in autoloader during class fetch should not cause UnwindExit string conversion error
+--FILE--
+<?php
+
+spl_autoload_register(function ($class) {
+    exit(0);
+});
+
+class A {
+    use NonExistentTrait;
+}
+
+echo "Should not reach here\n";
+?>
+--EXPECT--
diff --git a/Zend/zend_execute_API.c b/Zend/zend_execute_API.c
index 30eb6ec8af3d..b1a7f6befc5e 100644
--- a/Zend/zend_execute_API.c
+++ b/Zend/zend_execute_API.c
@@ -1719,6 +1719,12 @@ static ZEND_COLD void report_class_fetch_error(zend_string *class_name, uint32_t
 	}
 
 	if (EG(exception)) {
+		if (EG(exception) == (void *)(uintptr_t)-1) {
+			return;
+		}
+		if (zend_is_unwind_exit(EG(exception)) || zend_is_graceful_exit(EG(exception))) {
+			return;
+		}
 		if (!(fetch_type & ZEND_FETCH_CLASS_EXCEPTION)) {
 			zend_exception_uncaught_error("During class fetch");
 		}