diff --git a/os/backtrace.c b/os/backtrace.c
index 421d9fae4..aaa27d29e 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -90,13 +90,13 @@ print_registers(int frame, unw_cursor_t cursor)
     ErrorF("Registers at frame #%d:\n", frame);
 
     for (i = 0; i < num_regs; i++) {
-        uint64_t val;
+        unw_word_t val;
         ret = unw_get_reg(&cursor, regs[i].regnum, &val);
         if (ret < 0) {
             ErrorF("unw_get_reg(%s) failed: %s [%d]\n",
                           regs[i].name, unw_strerror(ret), ret);
         } else {
-            ErrorF("  %s: 0x%" PRIx64 "\n", regs[i].name, val);
+            ErrorF("  %s: 0x%" PRIxPTR "\n", regs[i].name, val);
         }
     }
 }