diff --git a/mm/ubsan/ubsan.c b/mm/ubsan/ubsan.c
index a306e37e86..c7f0f2462f 100644
--- a/mm/ubsan/ubsan.c
+++ b/mm/ubsan/ubsan.c
@@ -158,9 +158,11 @@ static int64_t get_signed_val(FAR struct type_descriptor *type,
   if (is_inline_int(type))
     {
       unsigned extra_bits = sizeof(int64_t) * 8 - type_bit_width(type);
-      uintptr_t ulong_val = (uintptr_t)val;
+      uint64_t mask = (1llu << extra_bits) - 1;
+      uint64_t ret = (uint64_t)val & mask;
 
-      return ((int64_t)ulong_val) << extra_bits >> extra_bits;
+      return (int64_t)(((ret & (1llu << (extra_bits - 1))) != 0) ?
+             ret | ~mask : ret);
     }
 
   return *(FAR int64_t *)val;