diff --git a/include/minix/com.h b/include/minix/com.h
index d11fbd135..3516d0be4 100644
--- a/include/minix/com.h
+++ b/include/minix/com.h
@@ -361,7 +361,6 @@
 #define PR_PS_STR_PTR   m1_p4	/* pointer to ps_strings, expected by __start */
 #define PR_FORK_FLAGS	m1_i3	/* optional flags for fork operation */
 #define PR_FORK_MSGADDR m1_p1	/* reply message address of forked child */
-#define PR_CTX_PTR	m1_p1	/* pointer to mcontext_t structure */
 
 /* Constants for exec. FIXME: these do not belong here. */
 #define PMEF_AUXVECTORS	20
diff --git a/include/minix/ipc.h b/include/minix/ipc.h
index e056658ec..f11364aeb 100644
--- a/include/minix/ipc.h
+++ b/include/minix/ipc.h
@@ -731,6 +731,14 @@ typedef struct {
 } mess_lsys_krn_sys_getinfo;
 _ASSERT_MSG_SIZE(mess_lsys_krn_sys_getinfo);
 
+typedef struct {
+	endpoint_t endpt;
+	vir_bytes ctx_ptr;
+
+	uint8_t padding[48];
+} mess_lsys_krn_sys_getmcontext;
+_ASSERT_MSG_SIZE(mess_lsys_krn_sys_getmcontext);
+
 typedef struct {
 	endpoint_t endpt;
 	int privflags;
@@ -803,6 +811,14 @@ typedef struct {
 } mess_lsys_krn_sys_setgrant;
 _ASSERT_MSG_SIZE(mess_lsys_krn_sys_setgrant);
 
+typedef struct {
+	endpoint_t endpt;
+	vir_bytes ctx_ptr;
+
+	uint8_t padding[48];
+} mess_lsys_krn_sys_setmcontext;
+_ASSERT_MSG_SIZE(mess_lsys_krn_sys_setmcontext);
+
 typedef struct {
 	int request;
 
@@ -1651,6 +1667,7 @@ typedef struct {
 		mess_lsys_krn_sys_abort m_lsys_krn_sys_abort;
 		mess_lsys_krn_sys_copy	m_lsys_krn_sys_copy;
 		mess_lsys_krn_sys_getinfo m_lsys_krn_sys_getinfo;
+		mess_lsys_krn_sys_getmcontext m_lsys_krn_sys_getmcontext;
 		mess_lsys_krn_sys_iopenable m_lsys_krn_sys_iopenable;
 		mess_lsys_krn_sys_irqctl m_lsys_krn_sys_irqctl;
 		mess_lsys_krn_sys_memset m_lsys_krn_sys_memset;
@@ -1658,6 +1675,7 @@ typedef struct {
 		mess_lsys_krn_sys_sdevio m_lsys_krn_sys_sdevio;
 		mess_lsys_krn_sys_setalarm m_lsys_krn_sys_setalarm;
 		mess_lsys_krn_sys_setgrant m_lsys_krn_sys_setgrant;
+		mess_lsys_krn_sys_setmcontext m_lsys_krn_sys_setmcontext;
 		mess_lsys_krn_sys_statectl m_lsys_krn_sys_statectl;
 		mess_lsys_krn_sys_stime	m_lsys_krn_sys_stime;
 		mess_lsys_krn_sys_settime m_lsys_krn_sys_settime;
diff --git a/kernel/system/do_mcontext.c b/kernel/system/do_mcontext.c
index e5d744901..db128b3c2 100644
--- a/kernel/system/do_mcontext.c
+++ b/kernel/system/do_mcontext.c
@@ -2,10 +2,13 @@
  *   m_type:	SYS_SETMCONTEXT
  *   m_type:	SYS_GETMCONTEXT
  *
- * The parameters for these kernel calls are:
- *     m1_i1:	PR_ENDPT        # proc endpoint doing call
- *     m1_p1:	PR_MEM_PTR	# pointer to mcontext structure
+ * The parameters for SYS_SETMCONTEXT kernel call are:
+ *   m_lsys_krn_sys_setmcontext.endpt	# proc endpoint doing call
+ *   m_lsys_krn_sys_setmcontext.ctx_ptr	# pointer to mcontext structure
  *
+ * The parameters for SYS_GETMCONTEXT kernel call are:
+ *   m_lsys_krn_sys_getmcontext.endpt	# proc endpoint doing call
+ *   m_lsys_krn_sys_getmcontext.ctx_ptr	# pointer to mcontext structure
  */
 
 #include "kernel/system.h"
@@ -25,7 +28,8 @@ int do_getmcontext(struct proc * caller, message * m_ptr)
   int proc_nr, r;
   mcontext_t mc;
 
-  if (! isokendpt(m_ptr->PR_ENDPT, &proc_nr)) return(EINVAL);
+  if (!isokendpt(m_ptr->m_lsys_krn_sys_getmcontext.endpt, &proc_nr))
+	return(EINVAL);
   if (iskerneln(proc_nr)) return(EPERM);
   rp = proc_addr(proc_nr);
 
@@ -35,7 +39,8 @@ int do_getmcontext(struct proc * caller, message * m_ptr)
 #endif
 
   /* Get the mcontext structure into our address space.  */
-  if ((r = data_copy(m_ptr->PR_ENDPT, (vir_bytes) m_ptr->PR_CTX_PTR, KERNEL,
+  if ((r = data_copy(m_ptr->m_lsys_krn_sys_getmcontext.endpt,
+		m_ptr->m_lsys_krn_sys_getmcontext.ctx_ptr, KERNEL,
 		(vir_bytes) &mc, (phys_bytes) sizeof(mcontext_t))) != OK)
 	return(r);
 
@@ -53,8 +58,9 @@ int do_getmcontext(struct proc * caller, message * m_ptr)
 
 
   /* Copy the mcontext structure to the user's address space. */
-  if ((r = data_copy(KERNEL, (vir_bytes) &mc, m_ptr->PR_ENDPT, 
-	(vir_bytes) m_ptr->PR_CTX_PTR,
+  if ((r = data_copy(KERNEL, (vir_bytes) &mc,
+	m_ptr->m_lsys_krn_sys_getmcontext.endpt,
+	m_ptr->m_lsys_krn_sys_getmcontext.ctx_ptr,
 	(phys_bytes) sizeof(mcontext_t))) != OK)
 	return(r);
 
@@ -73,11 +79,12 @@ int do_setmcontext(struct proc * caller, message * m_ptr)
   int proc_nr, r;
   mcontext_t mc;
 
-  if (!isokendpt(m_ptr->PR_ENDPT, &proc_nr)) return(EINVAL);
+  if (!isokendpt(m_ptr->m_lsys_krn_sys_setmcontext.endpt, &proc_nr)) return(EINVAL);
   rp = proc_addr(proc_nr);
 
   /* Get the mcontext structure into our address space.  */
-  if ((r = data_copy(m_ptr->PR_ENDPT, (vir_bytes) m_ptr->PR_CTX_PTR, KERNEL,
+  if ((r = data_copy(m_ptr->m_lsys_krn_sys_setmcontext.endpt,
+		m_ptr->m_lsys_krn_sys_setmcontext.ctx_ptr, KERNEL,
 		(vir_bytes) &mc, (phys_bytes) sizeof(mcontext_t))) != OK)
 	return(r);
 
diff --git a/lib/libsys/sys_mcontext.c b/lib/libsys/sys_mcontext.c
index 323304baa..087555fa9 100644
--- a/lib/libsys/sys_mcontext.c
+++ b/lib/libsys/sys_mcontext.c
@@ -9,8 +9,8 @@ vir_bytes mcp;			/* where to store context */
   message m;
   int r;
 
-  m.PR_ENDPT = proc;
-  m.PR_CTX_PTR = (char *) mcp;
+  m.m_lsys_krn_sys_getmcontext.endpt = proc;
+  m.m_lsys_krn_sys_getmcontext.ctx_ptr = mcp;
   r = _kernel_call(SYS_GETMCONTEXT, &m);
   return r;
 }
@@ -24,8 +24,8 @@ vir_bytes mcp;			/* where to get context from */
   message m;
   int r;
 
-  m.PR_ENDPT = proc;
-  m.PR_CTX_PTR = (char *) mcp;
+  m.m_lsys_krn_sys_setmcontext.endpt = proc;
+  m.m_lsys_krn_sys_setmcontext.ctx_ptr = mcp;
   r = _kernel_call(SYS_SETMCONTEXT, &m);
   return r;
 }