diff --git a/sys/amd64/amd64/db_disasm.c b/sys/amd64/amd64/db_disasm.c
index dd436d7d6bb4..0ec81f47fd44 100644
--- a/sys/amd64/amd64/db_disasm.c
+++ b/sys/amd64/amd64/db_disasm.c
@@ -1044,7 +1044,7 @@ db_read_address(loc, short_addr, rex, regmodrm, addrp)
 	    return (loc);
 	}
 	addrp->is_reg = FALSE;
-	addrp->index = 0;
+	addrp->index = NULL;
 
 	if (short_addr)
 	    size = LONG;
@@ -1067,7 +1067,7 @@ db_read_address(loc, short_addr, rex, regmodrm, addrp)
 		if (rm == 5) {
 		    get_value_inc(addrp->disp, loc, 4, FALSE);
 		    if (have_sib)
-			addrp->base = 0;
+			addrp->base = NULL;
 		    else if (short_addr)
 			addrp->base = "%eip";
 		    else
@@ -1109,9 +1109,9 @@ db_print_address(seg, size, rex, addrp)
 	    db_printf("%s:", seg);
 	}
 
-	if (addrp->disp != 0 || (addrp->base == 0 && addrp->index == 0))
+	if (addrp->disp != 0 || (addrp->base == NULL && addrp->index == NULL))
 		db_printsym((db_addr_t)addrp->disp, DB_STGY_ANY);
-	if (addrp->base != 0 || addrp->index != 0) {
+	if (addrp->base != NULL || addrp->index != NULL) {
 	    db_printf("(");
 	    if (addrp->base)
 		db_printf("%s", addrp->base);
@@ -1248,7 +1248,7 @@ db_disasm(db_addr_t loc, bool altfmt)
 	get_value_inc(inst, loc, 1, FALSE);
 	short_addr = FALSE;
 	size = LONG;
-	seg = 0;
+	seg = NULL;
 
 	/*
 	 * Get prefixes
@@ -1313,7 +1313,7 @@ db_disasm(db_addr_t loc, bool altfmt)
 	while (ip->i_size == ESC) {
 	    get_value_inc(inst, loc, 1, FALSE);
 	    ip = ((const struct inst * const *)ip->i_extra)[inst>>4];
-	    if (ip == 0) {
+	    if (ip == NULL) {
 		ip = &db_bad_inst;
 	    }
 	    else {
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 0351c551dfbb..6d984ab885e2 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -391,7 +391,7 @@ static struct md_page pv_dummy;
 /*
  * All those kernel PT submaps that BSD is so fond of
  */
-pt_entry_t *CMAP1 = 0;
+pt_entry_t *CMAP1 = NULL;
 caddr_t CADDR1 = 0;
 static vm_offset_t qframe = 0;
 static struct mtx qframe_mtx;
diff --git a/sys/boot/common/md.c b/sys/boot/common/md.c
index e81d1bb6e28e..22a0e953ad54 100644
--- a/sys/boot/common/md.c
+++ b/sys/boot/common/md.c
@@ -103,7 +103,7 @@ md_strategy(void *devdata, int rw, daddr_t blk, size_t size,
 	if ((ofs + size) > MD_IMAGE_SIZE)
 		size = MD_IMAGE_SIZE - ofs;
 
-	if (rsize != 0)
+	if (rsize != NULL)
 		*rsize = size;
 
 	switch (rw) {
diff --git a/sys/boot/efi/libefi/efinet.c b/sys/boot/efi/libefi/efinet.c
index 26802c2287d9..c598548ed9fc 100644
--- a/sys/boot/efi/libefi/efinet.c
+++ b/sys/boot/efi/libefi/efinet.c
@@ -131,13 +131,13 @@ efinet_put(struct iodesc *desc, void *pkt, size_t len)
 
 	/* Wait for the buffer to be transmitted */
 	do {
-		buf = 0;	/* XXX Is this needed? */
+		buf = NULL;	/* XXX Is this needed? */
 		status = net->GetStatus(net, 0, &buf);
 		/*
 		 * XXX EFI1.1 and the E1000 card returns a different 
 		 * address than we gave.  Sigh.
 		 */
-	} while (status == EFI_SUCCESS && buf == 0);
+	} while (status == EFI_SUCCESS && buf == NULL);
 
 	/* XXX How do we deal with status != EFI_SUCCESS now? */
 	return ((status == EFI_SUCCESS) ? len : -1);
diff --git a/sys/boot/fdt/fdt_overlay.c b/sys/boot/fdt/fdt_overlay.c
index a19f06e8e947..0d9b367d4639 100644
--- a/sys/boot/fdt/fdt_overlay.c
+++ b/sys/boot/fdt/fdt_overlay.c
@@ -64,7 +64,7 @@ fdt_get_fixup_location(void *fdtp, const char *fixup)
 	int prop_offset, o, proplen;
 	void  *result;
 
-	result = 0;
+	result = NULL;
 
 	path = strdup(fixup);
 	prop = strchr(path, ':');
diff --git a/sys/boot/ficl/ficl.c b/sys/boot/ficl/ficl.c
index d4370eb1a48a..219cf84b2225 100644
--- a/sys/boot/ficl/ficl.c
+++ b/sys/boot/ficl/ficl.c
@@ -276,7 +276,7 @@ void ficlFreeVM(FICL_VM *pVM)
     FICL_SYSTEM *pSys = pVM->pSys;
     FICL_VM *pList = pSys->vmList;
 
-    assert(pVM != 0);
+    assert(pVM != NULL);
 
     if (pSys->vmList == pVM)
     {
diff --git a/sys/boot/kshim/bsd_kernel.c b/sys/boot/kshim/bsd_kernel.c
index c94b755e9eaf..75eccb1d6725 100644
--- a/sys/boot/kshim/bsd_kernel.c
+++ b/sys/boot/kshim/bsd_kernel.c
@@ -75,7 +75,7 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
 	void *addr;
 
 	addr = malloc(dmat->maxsize + dmat->alignment, XXX, XXX);
-	if (addr == 0)
+	if (addr == NULL)
 		return (ENOMEM);
 
 	*mapp = addr;
diff --git a/sys/boot/ofw/libofw/ofw_memory.c b/sys/boot/ofw/libofw/ofw_memory.c
index 60cc90457bcb..5616184e8080 100644
--- a/sys/boot/ofw/libofw/ofw_memory.c
+++ b/sys/boot/ofw/libofw/ofw_memory.c
@@ -35,7 +35,7 @@ __FBSDID("$FreeBSD$");
 #include "libofw.h"
 #include "openfirm.h"
 
-static void		*heap_base = 0;
+static void		*heap_base = NULL;
 static unsigned int	heap_size = 0;
 
 struct ofw_mapping {
diff --git a/sys/boot/sparc64/loader/main.c b/sys/boot/sparc64/loader/main.c
index d7b4e1e7abbb..e70d9bbb0390 100644
--- a/sys/boot/sparc64/loader/main.c
+++ b/sys/boot/sparc64/loader/main.c
@@ -859,7 +859,7 @@ main(int (*openfirm)(void *))
 	/*
 	 * Initialize devices.
 	 */
-	for (dp = devsw; *dp != 0; dp++)
+	for (dp = devsw; *dp != NULL; dp++)
 		if ((*dp)->dv_init != 0)
 			(*dp)->dv_init();
 
diff --git a/sys/boot/userboot/userboot/userboot_disk.c b/sys/boot/userboot/userboot/userboot_disk.c
index 045854f12b62..e49393e9f082 100644
--- a/sys/boot/userboot/userboot/userboot_disk.c
+++ b/sys/boot/userboot/userboot/userboot_disk.c
@@ -91,8 +91,8 @@ userdisk_init(void)
 			return (ENOMEM);
 		for (i = 0; i < userdisk_maxunit; i++) {
 			if (CALLBACK(diskioctl, i, DIOCGSECTORSIZE,
-			    &sectorsize) != 0 || CALLBACK(diskioctl, i,
-			    DIOCGMEDIASIZE, &mediasize) != 0)
+			    &sectorsize) != NULL || CALLBACK(diskioctl, i,
+			    DIOCGMEDIASIZE, &mediasize) != NULL)
 				return (ENXIO);
 			ud_info[i].mediasize = mediasize;
 			ud_info[i].sectorsize = sectorsize;
diff --git a/sys/boot/zfs/zfs.c b/sys/boot/zfs/zfs.c
index 6cad2935616d..062895eef79a 100644
--- a/sys/boot/zfs/zfs.c
+++ b/sys/boot/zfs/zfs.c
@@ -126,7 +126,7 @@ zfs_close(struct open_file *f)
 {
 	struct file *fp = (struct file *)f->f_fsdata;
 
-	dnode_cache_obj = 0;
+	dnode_cache_obj = NULL;
 	f->f_fsdata = (void *)0;
 	if (fp == (struct file *)0)
 		return (0);
diff --git a/sys/boot/zfs/zfsimpl.c b/sys/boot/zfs/zfsimpl.c
index 8729a7517d1c..7f9063026959 100644
--- a/sys/boot/zfs/zfsimpl.c
+++ b/sys/boot/zfs/zfsimpl.c
@@ -69,7 +69,7 @@ static const char *features_for_read[] = {
 static spa_list_t zfs_pools;
 
 static uint64_t zfs_crc64_table[256];
-static const dnode_phys_t *dnode_cache_obj = 0;
+static const dnode_phys_t *dnode_cache_obj = NULL;
 static uint64_t dnode_cache_bn;
 static char *dnode_cache_buf;
 static char *zap_scratch;
@@ -1527,7 +1527,7 @@ fzap_lookup(const spa_t *spa, const dnode_phys_t *dnode, const char *name,
 	zc = &ZAP_LEAF_CHUNK(&zl, h);
 	while (zc->l_entry.le_hash != hash) {
 		if (zc->l_entry.le_next == 0xffff) {
-			zc = 0;
+			zc = NULL;
 			break;
 		}
 		zc = &ZAP_LEAF_CHUNK(&zl, zc->l_entry.le_next);
@@ -2316,7 +2316,7 @@ zfs_lookup(const struct zfsmount *mount, const char *upath, dnode_phys_t *dnode)
 			p = q;
 		} else {
 			strcpy(element, p);
-			p = 0;
+			p = NULL;
 		}
 
 		rc = zfs_dnode_stat(spa, &dn, &sb);
diff --git a/sys/libkern/iconv_xlat16.c b/sys/libkern/iconv_xlat16.c
index 630cbd3aff76..c423413b0b68 100644
--- a/sys/libkern/iconv_xlat16.c
+++ b/sys/libkern/iconv_xlat16.c
@@ -268,7 +268,7 @@ iconv_xlat16_conv(void *d2p, const char **inbuf,
 			 * there is a case that inbuf char is a single
 			 * byte char while inlen == 2
 			 */
-			if ((u_char)*(src+1) == 0 && !nullin ) {
+			if ((u_char)*(src+1) == '\0' && !nullin ) {
 				src++;
 				ir--;
 			} else {
diff --git a/sys/mips/atheros/ar531x/apb.c b/sys/mips/atheros/ar531x/apb.c
index a20ccc308705..cbf6776c6408 100644
--- a/sys/mips/atheros/ar531x/apb.c
+++ b/sys/mips/atheros/ar531x/apb.c
@@ -329,7 +329,7 @@ apb_alloc_resource(device_t bus, device_t child, int type, int *rid,
 	}
 
 	rv = rman_reserve_resource(rm, start, end, count, flags, child);
-	if (rv == 0) {
+	if (rv == NULL) {
 		printf("%s: could not reserve resource %d\n", __func__, type);
 		return (0);
 	}
diff --git a/sys/net/if_fddisubr.c b/sys/net/if_fddisubr.c
index 682a37caaea7..67a72c1f293e 100644
--- a/sys/net/if_fddisubr.c
+++ b/sys/net/if_fddisubr.c
@@ -400,7 +400,7 @@ fddi_input(ifp, m)
 	m_adj(m, FDDI_HDR_LEN);
 
 	m = m_pullup(m, LLC_SNAPFRAMELEN);
-	if (m == 0) {
+	if (m == NULL) {
 		if_inc_counter(ifp, IFCOUNTER_IERRORS, 1);
 		goto dropanyway;
 	}
diff --git a/sys/net/if_iso88025subr.c b/sys/net/if_iso88025subr.c
index e5d5166d60c4..32aac4cd4dd5 100644
--- a/sys/net/if_iso88025subr.c
+++ b/sys/net/if_iso88025subr.c
@@ -487,7 +487,7 @@ iso88025_input(ifp, m)
 	m_adj(m, mac_hdr_len);
 
 	m = m_pullup(m, LLC_SNAPFRAMELEN);
-	if (m == 0) {
+	if (m == NULL) {
 		if_inc_counter(ifp, IFCOUNTER_IERRORS, 1);
 		goto dropanyway;
 	}
diff --git a/sys/net/iflib.c b/sys/net/iflib.c
index e131dc46b1aa..34832c744e45 100644
--- a/sys/net/iflib.c
+++ b/sys/net/iflib.c
@@ -1003,7 +1003,7 @@ iflib_netmap_txq_init(if_ctx_t ctx, iflib_txq_t txq)
 	struct netmap_slot *slot;
 
 	slot = netmap_reset(na, NR_TX, txq->ift_id, 0);
-	if (slot == 0)
+	if (slot == NULL)
 		return;
 
 	for (int i = 0; i < ctx->ifc_softc_ctx.isc_ntxd[0]; i++) {
@@ -1028,7 +1028,7 @@ iflib_netmap_rxq_init(if_ctx_t ctx, iflib_rxq_t rxq)
 	int nrxd;
 
 	slot = netmap_reset(na, NR_RX, rxq->ifr_id, 0);
-	if (slot == 0)
+	if (slot == NULL)
 		return;
 	map = rxq->ifr_fl[0].ifl_sds.ifsd_map;
 	nrxd = ctx->ifc_softc_ctx.isc_nrxd[0];
diff --git a/sys/netpfil/ipfw/ip_fw_sockopt.c b/sys/netpfil/ipfw/ip_fw_sockopt.c
index 0823316e0884..4a8ffaacbcff 100644
--- a/sys/netpfil/ipfw/ip_fw_sockopt.c
+++ b/sys/netpfil/ipfw/ip_fw_sockopt.c
@@ -3135,7 +3135,7 @@ int
 classify_opcode_kidx(ipfw_insn *cmd, uint16_t *puidx)
 {
 
-	if (find_op_rw(cmd, puidx, NULL) == 0)
+	if (find_op_rw(cmd, puidx, NULL) == NULL)
 		return (1);
 	return (0);
 }