diff --git a/cpp2rust/cpp2rust.cpp b/cpp2rust/cpp2rust.cpp
index f7943b6f..2645f8f0 100644
--- a/cpp2rust/cpp2rust.cpp
+++ b/cpp2rust/cpp2rust.cpp
@@ -20,6 +20,17 @@
 
 #include "cpp2rust_lib.h"
 
+// LLVM's BumpPtrAllocator intentionally poisons freed slab memory via
+// __asan_poison_memory_region.  When ASan is enabled this can produce
+// use-after-poison false positives inside clang/LLVM itself (e.g. during
+// IdentifierTable initialisation).  Opting out of user-poisoning suppresses
+// those LLVM-internal false positives without affecting real UAF detection.
+#if defined(__has_feature) && __has_feature(address_sanitizer)
+extern "C" const char *__asan_default_options() {
+  return "allow_user_poisoning=0";
+}
+#endif
+
 namespace fs = std::filesystem;
 
 namespace {