diff --git a/sys/amd64/linux/linux_ptrace.c b/sys/amd64/linux/linux_ptrace.c
--- a/sys/amd64/linux/linux_ptrace.c
+++ b/sys/amd64/linux/linux_ptrace.c
@@ -524,7 +524,7 @@
 
 static int
 linux_ptrace_get_syscall_info(struct thread *td, pid_t pid,
-    l_ulong addr, l_ulong data)
+    l_ulong len, l_ulong data)
 {
 	struct ptrace_lwpinfo lwpinfo;
 	struct ptrace_sc_ret sr;
@@ -589,7 +589,8 @@
 	si.instruction_pointer = b_reg.r_rip;
 	si.stack_pointer = b_reg.r_rsp;
 
-	error = copyout(&si, (void *)data, sizeof(si));
+	len = MIN(len, sizeof(si));
+	error = copyout(&si, (void *)data, len);
 	if (error == 0)
 		td->td_retval[0] = sizeof(si);