diff --git a/Zend/zend_fibers.c b/Zend/zend_fibers.c
index 596a4f62069..1fde0453b9c 100644
--- a/Zend/zend_fibers.c
+++ b/Zend/zend_fibers.c
@@ -62,6 +62,7 @@
 #endif
 
 #ifdef __SANITIZE_ADDRESS__
+# include <sanitizer/asan_interface.h>
 # include <sanitizer/common_interface_defs.h>
 #endif
 
@@ -306,6 +307,12 @@ static void zend_fiber_stack_free(zend_fiber_stack *stack)
 
 	void *pointer = (void *) ((uintptr_t) stack->pointer - ZEND_FIBER_GUARD_PAGES * page_size);
 
+#ifdef __SANITIZE_ADDRESS__
+	/* If another mmap happens after unmapping, it may trigger the stale stack red zones
+	 * so we have to unpoison it before unmapping. */
+	ASAN_UNPOISON_MEMORY_REGION(pointer, stack->size + ZEND_FIBER_GUARD_PAGES * page_size);
+#endif
+
 #ifdef ZEND_WIN32
 	VirtualFree(pointer, 0, MEM_RELEASE);
 #else