diff --git a/libdl/libdl_cfi.cpp b/libdl/libdl_cfi.cpp
index 8458564..483364f 100644
--- a/libdl/libdl_cfi.cpp
+++ b/libdl/libdl_cfi.cpp
@@ -38,6 +38,11 @@
   return &shadow_base_storage.v;
 }
 
+// Returns the size of the CFI shadow mapping, or 0 if CFI is not (yet) used in this process.
+extern "C" size_t __cfi_shadow_size() {
+  return shadow_base_storage.v != 0 ? CFIShadow::kShadowSize : 0;
+}
+
 static uint16_t shadow_load(void* p) {
   uintptr_t addr = reinterpret_cast<uintptr_t>(p);
   uintptr_t ofs = CFIShadow::MemToShadowOffset(addr);