diff --git a/compiler-rt/lib/safestack/safestack.cc b/compiler-rt/lib/safestack/safestack.cc
--- a/compiler-rt/lib/safestack/safestack.cc
+++ b/compiler-rt/lib/safestack/safestack.cc
@@ -232,8 +232,7 @@
   SFS_CHECK((guard & (pageSize - 1)) == 0);
 
   void *addr = unsafe_stack_alloc(size, guard);
-  struct tinfo *tinfo =
-      (struct tinfo *)(((char *)addr) + size - sizeof(struct tinfo));
+  struct tinfo *tinfo = reinterpret_cast<struct tinfo *>(addr);
   tinfo->start_routine = start_routine;
   tinfo->start_routine_arg = arg;
   tinfo->unsafe_stack_start = addr;