diff --git a/tests/sys_ptrace_test.cpp b/tests/sys_ptrace_test.cpp
index bce5898..19c63fb 100644
--- a/tests/sys_ptrace_test.cpp
+++ b/tests/sys_ptrace_test.cpp
@@ -260,7 +260,7 @@
   ASSERT_EQ(0, sigaction(SIGALRM, &action, &oldaction)) << strerror(errno);
   alarm(5);
 
-  run_watchpoint_test<Uint128_t>(watchpoint_imprecise_child, 8, 8);
+  run_watchpoint_test<Uint128_t>(watchpoint_imprecise_child, 8, sizeof(void*));
 
   ASSERT_EQ(0, sigaction(SIGALRM, &oldaction, nullptr)) << strerror(errno);
 }