diff --git a/include/minix/callnr.h b/include/minix/callnr.h
index 8bcea61a1..5f15e58ff 100644
--- a/include/minix/callnr.h
+++ b/include/minix/callnr.h
@@ -64,12 +64,6 @@
 /* Field names for the exit(2) call. */
 #define PM_EXIT_STATUS		m1_i1	/* int */
 
-/* Field names for the ptrace(2) call. */
-#define PM_PTRACE_PID		m2_i1	/* pid_t */
-#define PM_PTRACE_REQ		m2_i2	/* int */
-#define PM_PTRACE_ADDR		m2_l1	/* long */
-#define PM_PTRACE_DATA		m2_l2	/* long */
-
 /* Field names for the sysuname(2) call. */
 #define PM_SYSUNAME_REQ		m1_i1	/* int */
 #define PM_SYSUNAME_FIELD	m1_i2	/* int */
diff --git a/include/minix/ipc.h b/include/minix/ipc.h
index 532b34408..f3f1075af 100644
--- a/include/minix/ipc.h
+++ b/include/minix/ipc.h
@@ -154,6 +154,23 @@ typedef struct {
 } mess_lc_pm_itimer;
 _ASSERT_MSG_SIZE(mess_lc_pm_itimer);
 
+typedef struct {
+	pid_t pid;
+	int req;
+	vir_bytes addr;
+	long data;
+
+	uint8_t padding[40];
+} mess_lc_pm_ptrace;
+_ASSERT_MSG_SIZE(mess_lc_pm_ptrace);
+
+typedef struct {
+	long data;
+
+	uint8_t padding[52];
+} mess_pm_lc_ptrace;
+_ASSERT_MSG_SIZE(mess_pm_lc_ptrace);
+
 typedef struct {
 	time_t sec;
 
@@ -932,6 +949,7 @@ typedef struct {
 		mess_fs_vfs_readwrite	m_fs_vfs_readwrite;
 
 		mess_lc_pm_itimer	m_lc_pm_itimer;
+		mess_lc_pm_ptrace	m_lc_pm_ptrace;
 		mess_lc_pm_time		m_lc_pm_time;
 		mess_lc_pm_waitpid	m_lc_pm_waitpid;
 
@@ -967,6 +985,7 @@ typedef struct {
 		mess_lsys_vfs_copyfd	m_lsys_vfs_copyfd;
 		mess_lsys_vfs_mapdriver	m_lsys_vfs_mapdriver;
 
+		mess_pm_lc_ptrace	m_pm_lc_ptrace;
 		mess_pm_lc_time		m_pm_lc_time;
 		mess_pm_lc_waitpid	m_pm_lc_waitpid;
 
diff --git a/lib/libc/sys-minix/ptrace.c b/lib/libc/sys-minix/ptrace.c
index 77d8279ea..9dd63a9d3 100644
--- a/lib/libc/sys-minix/ptrace.c
+++ b/lib/libc/sys-minix/ptrace.c
@@ -10,16 +10,16 @@ int ptrace(int req, pid_t pid, void *addr, int data)
   message m;
 
   memset(&m, 0, sizeof(m));
-  m.PM_PTRACE_PID = pid;
-  m.PM_PTRACE_REQ = req;
-  m.PM_PTRACE_ADDR = addr;
-  m.PM_PTRACE_DATA = data;
+  m.m_lc_pm_ptrace.pid = pid;
+  m.m_lc_pm_ptrace.req = req;
+  m.m_lc_pm_ptrace.addr = addr;
+  m.m_lc_pm_ptrace.data = data;
   if (_syscall(PM_PROC_NR, PM_PTRACE, &m) < 0) return(-1);
 
   /* There was no error, but -1 is a legal return value.  Clear errno if
    * necessary to distinguish this case.  _syscall has set errno to nonzero
    * for the error case.
    */
-  if (m.PM_PTRACE_DATA == -1) errno = 0;
-  return(m.PM_PTRACE_DATA);
+  if (m.m_pm_lc_ptrace.data == -1) errno = 0;
+  return(m.m_pm_lc_ptrace.data);
 }
diff --git a/servers/pm/forkexit.c b/servers/pm/forkexit.c
index 93f6dd032..85ffb6f36 100644
--- a/servers/pm/forkexit.c
+++ b/servers/pm/forkexit.c
@@ -437,7 +437,7 @@ int dump_core;			/* flag indicating whether to dump core */
   if (rmp->mp_flags & TRACE_EXIT)
   {
 	/* Wake up the tracer, completing the ptrace(T_EXIT) call */
-	mproc[rmp->mp_tracer].mp_reply.PM_PTRACE_DATA = 0;
+	mproc[rmp->mp_tracer].mp_reply.m_pm_lc_ptrace.data = 0;
 	reply(rmp->mp_tracer, OK);
   }
 
diff --git a/servers/pm/trace.c b/servers/pm/trace.c
index 850b16acb..6d11a4762 100644
--- a/servers/pm/trace.c
+++ b/servers/pm/trace.c
@@ -44,7 +44,7 @@ int do_trace()
   struct ptrace_range pr;
   int i, r, req;
 
-  req = m_in.PM_PTRACE_REQ;
+  req = m_in.m_lc_pm_ptrace.req;
 
   /* The T_OK call is made by the child fork of the debugger before it execs
    * the process to be traced. The T_ATTACH call is made by the debugger itself
@@ -55,11 +55,11 @@ int do_trace()
 	if (mp->mp_tracer != NO_TRACER) return(EBUSY);
 
 	mp->mp_tracer = mp->mp_parent;
-	mp->mp_reply.PM_PTRACE_DATA = 0;
+	mp->mp_reply.m_pm_lc_ptrace.data = 0;
 	return(OK);
 
   case T_ATTACH:	/* attach to an existing process */
-	if ((child = find_proc(m_in.PM_PTRACE_PID)) == NULL) return(ESRCH);
+	if ((child = find_proc(m_in.m_lc_pm_ptrace.pid)) == NULL) return(ESRCH);
 	if (child->mp_flags & EXITING) return(ESRCH);
 
 	/* For non-root processes, user and group ID must match. */
@@ -88,7 +88,7 @@ int do_trace()
 
 	sig_proc(child, SIGSTOP, TRUE /*trace*/, FALSE /* ksig */);
 
-	mp->mp_reply.PM_PTRACE_DATA = 0;
+	mp->mp_reply.m_pm_lc_ptrace.data = 0;
 	return(OK);
 
   case T_STOP:		/* stop the process */
@@ -99,19 +99,19 @@ int do_trace()
 
   case T_READB_INS:	/* special hack for reading text segments */
 	if (mp->mp_effuid != SUPER_USER) return(EPERM);
-	if ((child = find_proc(m_in.PM_PTRACE_PID)) == NULL) return(ESRCH);
+	if ((child = find_proc(m_in.m_lc_pm_ptrace.pid)) == NULL) return(ESRCH);
 	if (child->mp_flags & EXITING) return(ESRCH);
 
-	r = sys_trace(req, child->mp_endpoint, m_in.PM_PTRACE_ADDR,
-		&m_in.PM_PTRACE_DATA);
+	r = sys_trace(req, child->mp_endpoint, m_in.m_lc_pm_ptrace.addr,
+		&m_in.m_lc_pm_ptrace.data);
 	if (r != OK) return(r);
 
-	mp->mp_reply.PM_PTRACE_DATA = m_in.PM_PTRACE_DATA;
+	mp->mp_reply.m_pm_lc_ptrace.data = m_in.m_lc_pm_ptrace.data;
 	return(OK);
 
   case T_WRITEB_INS:	/* special hack for patching text segments */
 	if (mp->mp_effuid != SUPER_USER) return(EPERM);
-	if ((child = find_proc(m_in.PM_PTRACE_PID)) == NULL) return(ESRCH);
+	if ((child = find_proc(m_in.m_lc_pm_ptrace.pid)) == NULL) return(ESRCH);
 	if (child->mp_flags & EXITING) return(ESRCH);
 
 #if 0
@@ -125,18 +125,18 @@ int do_trace()
 	child->mp_ctime = 0;
 #endif
 
-	r = sys_trace(req, child->mp_endpoint, m_in.PM_PTRACE_ADDR,
-		&m_in.PM_PTRACE_DATA);
+	r = sys_trace(req, child->mp_endpoint, m_in.m_lc_pm_ptrace.addr,
+		&m_in.m_lc_pm_ptrace.data);
 	if (r != OK) return(r);
 
-	mp->mp_reply.PM_PTRACE_DATA = m_in.PM_PTRACE_DATA;
+	mp->mp_reply.m_pm_lc_ptrace.data = m_in.m_lc_pm_ptrace.data;
 	return(OK);
   }
 
   /* All the other calls are made by the tracing process to control execution
    * of the child. For all these calls, the child must be stopped.
    */
-  if ((child = find_proc(m_in.PM_PTRACE_PID)) == NULL) return(ESRCH);
+  if ((child = find_proc(m_in.m_lc_pm_ptrace.pid)) == NULL) return(ESRCH);
   if (child->mp_flags & EXITING) return(ESRCH);
   if (child->mp_tracer != who_p) return(ESRCH);
   if (!(child->mp_flags & TRACE_STOPPED)) return(EBUSY);
@@ -147,9 +147,9 @@ int do_trace()
 
 	/* Defer the exit if the traced process has an VFS call pending. */
 	if (child->mp_flags & VFS_CALL)
-		child->mp_exitstatus = (int) m_in.PM_PTRACE_DATA; /* save it */
+		child->mp_exitstatus = m_in.m_lc_pm_ptrace.data; /* save it */
 	else
-		exit_proc(child, (int) m_in.PM_PTRACE_DATA,
+		exit_proc(child, m_in.m_lc_pm_ptrace.data,
 			FALSE /*dump_core*/);
 
 	/* Do not reply to the caller until VFS has processed the exit
@@ -158,15 +158,15 @@ int do_trace()
 	return(SUSPEND);
 
   case T_SETOPT:	/* set trace options */
-	child->mp_trace_flags = m_in.PM_PTRACE_DATA;
+	child->mp_trace_flags = m_in.m_lc_pm_ptrace.data;
 
-	mp->mp_reply.PM_PTRACE_DATA = 0;
+	mp->mp_reply.m_pm_lc_ptrace.data = 0;
 	return(OK);
 
   case T_GETRANGE:
   case T_SETRANGE:	/* get/set range of values */
-	r = sys_datacopy(who_e, (vir_bytes) m_in.PM_PTRACE_ADDR,
-			SELF, (vir_bytes) &pr, (phys_bytes) sizeof(pr));
+	r = sys_datacopy(who_e, m_in.m_lc_pm_ptrace.addr, SELF, (vir_bytes)&pr,
+		(phys_bytes)sizeof(pr));
 	if (r != OK) return(r);
 
 	if (pr.pr_space != TS_INS && pr.pr_space != TS_DATA) return(EINVAL);
@@ -183,11 +183,11 @@ int do_trace()
 
 	if (r != OK) return(r);
 
-	mp->mp_reply.PM_PTRACE_DATA = 0;
+	mp->mp_reply.m_pm_lc_ptrace.data = 0;
 	return(OK);
 
   case T_DETACH:	/* detach from traced process */
-	if (m_in.PM_PTRACE_DATA < 0 || m_in.PM_PTRACE_DATA >= _NSIG)
+	if (m_in.m_lc_pm_ptrace.data < 0 || m_in.m_lc_pm_ptrace.data >= _NSIG)
 		return(EINVAL);
 
 	child->mp_tracer = NO_TRACER;
@@ -200,8 +200,8 @@ int do_trace()
 		}
 	}
 
-	if (m_in.PM_PTRACE_DATA > 0) {		/* issue signal */
-		sig_proc(child, (int) m_in.PM_PTRACE_DATA, TRUE /*trace*/,
+	if (m_in.m_lc_pm_ptrace.data > 0) {		/* issue signal */
+		sig_proc(child, m_in.m_lc_pm_ptrace.data, TRUE /*trace*/,
 			FALSE /* ksig */);
 	}
 
@@ -216,11 +216,11 @@ int do_trace()
   case T_RESUME: 
   case T_STEP:
   case T_SYSCALL:	/* resume execution */
-	if (m_in.PM_PTRACE_DATA < 0 || m_in.PM_PTRACE_DATA >= _NSIG)
+	if (m_in.m_lc_pm_ptrace.data < 0 || m_in.m_lc_pm_ptrace.data >= _NSIG)
 		return(EINVAL);
 
-	if (m_in.PM_PTRACE_DATA > 0) {		/* issue signal */
-		sig_proc(child, (int) m_in.PM_PTRACE_DATA, FALSE /*trace*/,
+	if (m_in.m_lc_pm_ptrace.data > 0) {		/* issue signal */
+		sig_proc(child, m_in.m_lc_pm_ptrace.data, FALSE /*trace*/,
 			FALSE /* ksig */);
 	}
 
@@ -229,7 +229,7 @@ int do_trace()
 	 */
 	for (i = 1; i < _NSIG; i++) {
 		if (sigismember(&child->mp_sigtrace, i)) {
-			mp->mp_reply.PM_PTRACE_DATA = 0;
+			mp->mp_reply.m_pm_lc_ptrace.data = 0;
 			return(OK);
 		}
 	}
@@ -240,11 +240,11 @@ int do_trace()
 
 	break;
   }
-  r = sys_trace(req, child->mp_endpoint, m_in.PM_PTRACE_ADDR,
-	&m_in.PM_PTRACE_DATA);
+  r = sys_trace(req, child->mp_endpoint, m_in.m_lc_pm_ptrace.addr,
+	&m_in.m_lc_pm_ptrace.data);
   if (r != OK) return(r);
 
-  mp->mp_reply.PM_PTRACE_DATA = m_in.PM_PTRACE_DATA;
+  mp->mp_reply.m_pm_lc_ptrace.data = m_in.m_lc_pm_ptrace.data;
   return(OK);
 }