diff --git a/sys/alpha/alpha/mp_machdep.c b/sys/alpha/alpha/mp_machdep.c
index 7595330ea02d..b18c79c5e3f6 100644
--- a/sys/alpha/alpha/mp_machdep.c
+++ b/sys/alpha/alpha/mp_machdep.c
@@ -339,7 +339,6 @@ cpu_mp_setmaxid(void)
 			continue;
 		mp_maxid = i;
 	}
-	mp_maxid++;
 }
 
 int
diff --git a/sys/amd64/amd64/mp_machdep.c b/sys/amd64/amd64/mp_machdep.c
index d203cbe376f5..0d4ddf8e553e 100644
--- a/sys/amd64/amd64/mp_machdep.c
+++ b/sys/amd64/amd64/mp_machdep.c
@@ -179,8 +179,8 @@ cpu_add(u_int apic_id, char boot_cpu)
 		cpu_info[apic_id].cpu_bsp = 1;
 	}
 	mp_ncpus++;
-	if (apic_id >= mp_maxid)
-		mp_maxid = apic_id + 1;
+	if (apic_id > mp_maxid)
+		mp_maxid = apic_id;
 	if (bootverbose)
 		printf("SMP: Added CPU %d (%s)\n", apic_id, boot_cpu ? "BSP" :
 		    "AP");
diff --git a/sys/i386/i386/mp_machdep.c b/sys/i386/i386/mp_machdep.c
index 578eb22548db..a2c4b48ed1c9 100644
--- a/sys/i386/i386/mp_machdep.c
+++ b/sys/i386/i386/mp_machdep.c
@@ -258,7 +258,7 @@ void
 cpu_mp_setmaxid(void)
 {
 
-	mp_maxid = MAXCPU;
+	mp_maxid = MAXCPU - 1;
 }
 
 int
diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index b42be6d5f7db..6e18ecb33f54 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -418,7 +418,7 @@ sched_balance(void *arg)
 	if (smp_started == 0)
 		goto out;
 
-	for (i = 0; i < mp_maxid; i++) {
+	for (i = 0; i <= mp_maxid; i++) {
 		if (CPU_ABSENT(i) || (i & stopped_cpus) != 0)
 			continue;
 		kseq = KSEQ_CPU(i);
diff --git a/sys/sparc64/sparc64/mp_machdep.c b/sys/sparc64/sparc64/mp_machdep.c
index c26f6f75d641..8625b436bda9 100644
--- a/sys/sparc64/sparc64/mp_machdep.c
+++ b/sys/sparc64/sparc64/mp_machdep.c
@@ -159,14 +159,14 @@ cpu_mp_setmaxid(void)
 		    strcmp(buf, "cpu") == 0)
 			cpus++;
 	}
-	mp_maxid = cpus;
+	mp_maxid = cpus - 1;
 }
 
 int
 cpu_mp_probe(void)
 {
 
-	return (mp_maxid > 1);
+	return (mp_maxid > 0);
 }
 
 static void
diff --git a/sys/sys/smp.h b/sys/sys/smp.h
index cd96ebe14f16..519e917698a2 100644
--- a/sys/sys/smp.h
+++ b/sys/sys/smp.h
@@ -81,7 +81,7 @@ extern volatile int smp_started;
  * The cpu_setmaxid() function is called very early during the boot process
  * so that the MD code may set mp_maxid to provide an upper bound on CPU IDs
  * that other subsystems may use.  If a platform is not able to determine
- * the exact maximum ID that early, then it may set mp_maxid to MAXCPU.
+ * the exact maximum ID that early, then it may set mp_maxid to MAXCPU - 1.
  */
 struct thread;
 
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 4aa5576cafd4..b1d0008fc86d 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -126,14 +126,6 @@ static int uma_boot_free = 0;
 /* Is the VM done starting up? */
 static int booted = 0;
 
-/*
- * Rather than #ifdef SMP all over, just give us a bogus definition for
- * this on UP.
- */
-#ifndef SMP
-static int mp_maxid = 1;
-#endif
-
 /*
  * This is the handle used to schedule events that need to happen
  * outside of the allocation fast path.
@@ -350,7 +342,7 @@ zone_timeout(uma_zone_t zone)
 	 * far out of sync.
 	 */
 	if (!(zone->uz_flags & UMA_ZFLAG_INTERNAL)) {
-		for (cpu = 0; cpu < mp_maxid; cpu++) {
+		for (cpu = 0; cpu <= mp_maxid; cpu++) {
 			if (CPU_ABSENT(cpu))
 				continue;
 			CPU_LOCK(cpu); 
@@ -577,7 +569,7 @@ cache_drain(uma_zone_t zone)
 	/*
 	 * We have to lock each cpu cache before locking the zone
 	 */
-	for (cpu = 0; cpu < mp_maxid; cpu++) {
+	for (cpu = 0; cpu <= mp_maxid; cpu++) {
 		if (CPU_ABSENT(cpu))
 			continue;
 		CPU_LOCK(cpu);
@@ -609,7 +601,7 @@ cache_drain(uma_zone_t zone)
 		LIST_REMOVE(bucket, ub_link);
 		bucket_free(bucket);
 	}
-	for (cpu = 0; cpu < mp_maxid; cpu++) {
+	for (cpu = 0; cpu <= mp_maxid; cpu++) {
 		if (CPU_ABSENT(cpu))
 			continue;
 		CPU_UNLOCK(cpu);
@@ -1228,7 +1220,7 @@ uma_startup(void *bootmem)
 	/* "manually" Create the initial zone */
 	args.name = "UMA Zones";
 	args.size = sizeof(struct uma_zone) +
-	    (sizeof(struct uma_cache) * mp_maxid);
+	    (sizeof(struct uma_cache) * (mp_maxid + 1));
 	args.ctor = zone_ctor;
 	args.dtor = zone_dtor;
 	args.uminit = zero_init;
@@ -1239,7 +1231,7 @@ uma_startup(void *bootmem)
 	zone_ctor(zones, sizeof(struct uma_zone), &args);
 
 	/* Initialize the pcpu cache lock set once and for all */
-	for (i = 0; i < mp_maxid; i++)
+	for (i = 0; i <= mp_maxid; i++)
 		CPU_LOCK_INIT(i);
 #ifdef UMA_DEBUG
 	printf("Filling boot free list.\n");
@@ -2105,7 +2097,7 @@ uma_print_zone(uma_zone_t zone)
 	printf("Full slabs:\n");
 	LIST_FOREACH(slab, &zone->uz_full_slab, us_link)
 		slab_print(slab);
-	for (i = 0; i < mp_maxid; i++) {
+	for (i = 0; i <= mp_maxid; i++) {
 		if (CPU_ABSENT(i))
 			continue;
 		cache = &zone->uz_cpu[i];
@@ -2153,7 +2145,7 @@ sysctl_vm_zone(SYSCTL_HANDLER_ARGS)
 		if (cnt == 0)	/* list may have changed size */
 			break;
 		if (!(z->uz_flags & UMA_ZFLAG_INTERNAL)) {
-			for (cpu = 0; cpu < mp_maxid; cpu++) {
+			for (cpu = 0; cpu <= mp_maxid; cpu++) {
 				if (CPU_ABSENT(cpu))
 					continue;
 				CPU_LOCK(cpu);
@@ -2162,7 +2154,7 @@ sysctl_vm_zone(SYSCTL_HANDLER_ARGS)
 		ZONE_LOCK(z);
 		cachefree = 0;
 		if (!(z->uz_flags & UMA_ZFLAG_INTERNAL)) {
-			for (cpu = 0; cpu < mp_maxid; cpu++) {
+			for (cpu = 0; cpu <= mp_maxid; cpu++) {
 				if (CPU_ABSENT(cpu))
 					continue;
 				cache = &z->uz_cpu[cpu];