diff --git a/servers/pm/main.c b/servers/pm/main.c
index aaa2d6bab..90da3812f 100644
--- a/servers/pm/main.c
+++ b/servers/pm/main.c
@@ -207,6 +207,7 @@ PRIVATE int sef_cb_init_fresh(int type, sef_init_info_t *info)
   /* Initialize process table, including timers. */
   for (rmp=&mproc[0]; rmp<&mproc[NR_PROCS]; rmp++) {
 	init_timer(&rmp->mp_timer);
+	rmp->mp_magic = MP_MAGIC;
   }
 
   /* Build the set of signals which cause core dumps, and the set of signals
diff --git a/servers/pm/mproc.h b/servers/pm/mproc.h
index ce6fff9af..e841f0152 100644
--- a/servers/pm/mproc.h
+++ b/servers/pm/mproc.h
@@ -8,6 +8,8 @@
 #include <timers.h>
 #include <signal.h>
 
+#include <sys/cdefs.h>
+
 /* Needs to be included here, for 'ps' etc */
 #include "const.h"
 
@@ -44,6 +46,9 @@ EXTERN struct mproc {
   sigset_t mp_ksigpending;	/* bitmap for pending signals from the kernel */
   sigset_t mp_sigtrace;		/* signals to hand to tracer first */
   struct sigaction mp_sigact[_NSIG]; /* as in sigaction(2) */
+#ifdef __ACK__
+  char mp_padding[60];		/* align structure with new libc */
+#endif
   vir_bytes mp_sigreturn; 	/* address of C library __sigreturn function */
   struct timer mp_timer;	/* watchdog timer for alarm(2), setitimer(2) */
   clock_t mp_interval[NR_ITIMERS];	/* setitimer(2) repetition intervals */
@@ -63,6 +68,8 @@ EXTERN struct mproc {
   endpoint_t mp_scheduler;	/* scheduler endpoint id */
 
   char mp_name[PROC_NAME_LEN];	/* process name */
+
+  int mp_magic;			/* sanity check, MP_MAGIC */
 } mproc[NR_PROCS];
 
 /* Flag values */
@@ -85,4 +92,4 @@ EXTERN struct mproc {
 #define TRACE_ZOMBIE	0x10000	/* waiting for tracer to issue WAIT call */
 #define DELAY_CALL	0x20000	/* waiting for call before sending signal */
 
-
+#define MP_MAGIC	0xC0FFEE0
diff --git a/servers/procfs/tree.c b/servers/procfs/tree.c
index 9b4478ec6..e71513fea 100644
--- a/servers/procfs/tree.c
+++ b/servers/procfs/tree.c
@@ -77,6 +77,22 @@ PRIVATE int dir_is_pid(struct inode *node)
 		get_inode_index(node) != NO_INDEX);
 }
 
+PRIVATE int mproc_ok(struct mproc *tab, int slots)
+{
+	int i;
+
+	/* sanity check of mproc */
+
+	for(i = 0; i < slots; i++) {
+		if(tab[i].mp_magic != MP_MAGIC) {
+			printf("procfs: mproc table magic number mismatch\n");
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
 /*===========================================================================*
  *				update_tables				     *
  *===========================================================================*/
@@ -99,6 +115,8 @@ PRIVATE int update_tables(void)
 
 	if ((r = getsysinfo(PM_PROC_NR, SI_PROC_TAB, mproc)) != OK) return r;
 
+	if(!mproc_ok(mproc, NR_PROCS)) return EINVAL;
+
 	if ((r = getsysinfo(VFS_PROC_NR, SI_PROC_TAB, fproc)) != OK) return r;
 
 	return OK;