diff --git a/usr.sbin/sade/menus.c b/usr.sbin/sade/menus.c
index b56a8e2ea24f..71bc616c6035 100644
--- a/usr.sbin/sade/menus.c
+++ b/usr.sbin/sade/menus.c
@@ -1342,7 +1342,7 @@ DMenu MenuConfigure = {
 	NULL,	dmenuSubmenu, NULL, &MenuMedia },
 #ifdef WITH_MICE
       { " Mouse",	"Configure your mouse",
-	NULL,	dmenuSubmenu, NULL, &MenuMouse, NULL },
+	NULL,	dmenuSubmenu, NULL, &MenuMouse },
 #endif
       { " Networking",	"Configure additional network services",
 	NULL,	dmenuSubmenu, NULL, &MenuNetworking },
diff --git a/usr.sbin/sade/sade.h b/usr.sbin/sade/sade.h
index e4c939f4ec60..938cfad0be72 100644
--- a/usr.sbin/sade/sade.h
+++ b/usr.sbin/sade/sade.h
@@ -871,7 +871,7 @@ extern void	slice_wizard(Disk *d);
 /*
  * Macros.  Please find a better place for us!
  */
-#define DEVICE_INIT(d)		((d) != NULL ? (d)->init((d)) : NULL)
+#define DEVICE_INIT(d)		((d) != NULL ? (d)->init((d)) : (Boolean)0)
 #define DEVICE_GET(d, b, f)	((d) != NULL ? (d)->get((d), (b), (f)) : NULL)
 #define DEVICE_SHUTDOWN(d)	((d) != NULL ? (d)->shutdown((d)) : (void)0)
 
diff --git a/usr.sbin/sade/system.c b/usr.sbin/sade/system.c
index 906dec206061..65c353a41c9e 100644
--- a/usr.sbin/sade/system.c
+++ b/usr.sbin/sade/system.c
@@ -140,7 +140,7 @@ systemInitialize(int argc, char **argv)
     globalsInit();
 
     i = sizeof(boothowto);
-    if (!sysctlbyname("debug.boothowto", &boothowto, &i, NULL, NULL) &&
+    if (!sysctlbyname("debug.boothowto", &boothowto, &i, NULL, 0) &&
         (i == sizeof(boothowto)) && (boothowto & RB_VERBOSE))
 	variable_set2(VAR_DEBUG, "YES", 0);
 
diff --git a/usr.sbin/sade/variable.c b/usr.sbin/sade/variable.c
index e1328629d8a1..e86104fd100a 100644
--- a/usr.sbin/sade/variable.c
+++ b/usr.sbin/sade/variable.c
@@ -205,7 +205,7 @@ variable_check2(char *data)
 	    *cp3 = '\0';
         cp2 = variable_get(tmp);
         if (cp2 != NULL) {
-	    if (*cp == NULL)
+	    if (*cp == '\0')
 		return 2;
 	    else
 		return strcmp(cp, cp2) == 0 ? 1 : 0;
diff --git a/usr.sbin/sysinstall/anonFTP.c b/usr.sbin/sysinstall/anonFTP.c
index f79974b56b9c..7d130f14e95d 100644
--- a/usr.sbin/sysinstall/anonFTP.c
+++ b/usr.sbin/sysinstall/anonFTP.c
@@ -115,7 +115,7 @@ static Layout layout[] = {
     { 19, 35, 0, 0,
       "CANCEL", "Select this if you wish to cancel this screen",
       &cancelbutton, BUTTONOBJ, NULL },
-    { NULL },
+    { 0 },
 };
 
 static int
diff --git a/usr.sbin/sysinstall/dhcp.c b/usr.sbin/sysinstall/dhcp.c
index a74a72bd4ba6..fa35580e1235 100644
--- a/usr.sbin/sysinstall/dhcp.c
+++ b/usr.sbin/sysinstall/dhcp.c
@@ -89,7 +89,7 @@ dhcpParseLeases(char *file, char *hostname, char *domain, char *nameserver,
 		continue;
 	    }
 	    if ((tptr = (char *)strchr(tempbuf, ';')) && (*(tptr + 1) == 0)) {
-		*tptr = NULL;
+		*tptr = '\0';
 		endedflag = 1;
 	    }
 	    if (!isalnum(tempbuf[0])) {
@@ -114,7 +114,7 @@ dhcpParseLeases(char *file, char *hostname, char *domain, char *nameserver,
 		continue;
 	    }
 	    if ((tptr = (char *)strchr(tempbuf, ';')) && (*(tptr + 1) == 0)) {
-		*tptr = NULL;
+		*tptr = '\0';
 		endedflag = 1;
 	    }
 	    if (tempbuf[0] == '"') {
@@ -135,14 +135,14 @@ dhcpParseLeases(char *file, char *hostname, char *domain, char *nameserver,
 		strcpy(ipaddr, optbuf);
 	    } else if (!strcasecmp("routers", optname)) {
 		if((tptr = (char *)strchr(optbuf, ',')))
-		    *tptr = NULL;
+		    *tptr = '\0';
 		strcpy(gateway, optbuf);
 	    } else if (!strcasecmp("subnet-mask", optname)) {
 		strcpy(netmask, optbuf);
 	    } else if (!strcasecmp("domain-name-servers", optname)) {
 		/* <jkh> ...one value per property */
 		if((tptr = (char *)strchr(optbuf, ',')))
-		    *tptr = NULL;
+		    *tptr = '\0';
 		strcpy(nameserver, optbuf);
 	    }
 	    if (endedflag) {
diff --git a/usr.sbin/sysinstall/menus.c b/usr.sbin/sysinstall/menus.c
index b56a8e2ea24f..71bc616c6035 100644
--- a/usr.sbin/sysinstall/menus.c
+++ b/usr.sbin/sysinstall/menus.c
@@ -1342,7 +1342,7 @@ DMenu MenuConfigure = {
 	NULL,	dmenuSubmenu, NULL, &MenuMedia },
 #ifdef WITH_MICE
       { " Mouse",	"Configure your mouse",
-	NULL,	dmenuSubmenu, NULL, &MenuMouse, NULL },
+	NULL,	dmenuSubmenu, NULL, &MenuMouse },
 #endif
       { " Networking",	"Configure additional network services",
 	NULL,	dmenuSubmenu, NULL, &MenuNetworking },
diff --git a/usr.sbin/sysinstall/sysinstall.h b/usr.sbin/sysinstall/sysinstall.h
index e4c939f4ec60..938cfad0be72 100644
--- a/usr.sbin/sysinstall/sysinstall.h
+++ b/usr.sbin/sysinstall/sysinstall.h
@@ -871,7 +871,7 @@ extern void	slice_wizard(Disk *d);
 /*
  * Macros.  Please find a better place for us!
  */
-#define DEVICE_INIT(d)		((d) != NULL ? (d)->init((d)) : NULL)
+#define DEVICE_INIT(d)		((d) != NULL ? (d)->init((d)) : (Boolean)0)
 #define DEVICE_GET(d, b, f)	((d) != NULL ? (d)->get((d), (b), (f)) : NULL)
 #define DEVICE_SHUTDOWN(d)	((d) != NULL ? (d)->shutdown((d)) : (void)0)
 
diff --git a/usr.sbin/sysinstall/system.c b/usr.sbin/sysinstall/system.c
index 906dec206061..65c353a41c9e 100644
--- a/usr.sbin/sysinstall/system.c
+++ b/usr.sbin/sysinstall/system.c
@@ -140,7 +140,7 @@ systemInitialize(int argc, char **argv)
     globalsInit();
 
     i = sizeof(boothowto);
-    if (!sysctlbyname("debug.boothowto", &boothowto, &i, NULL, NULL) &&
+    if (!sysctlbyname("debug.boothowto", &boothowto, &i, NULL, 0) &&
         (i == sizeof(boothowto)) && (boothowto & RB_VERBOSE))
 	variable_set2(VAR_DEBUG, "YES", 0);
 
diff --git a/usr.sbin/sysinstall/tcpip.c b/usr.sbin/sysinstall/tcpip.c
index 2f9dc8da85c6..db1539d0e376 100644
--- a/usr.sbin/sysinstall/tcpip.c
+++ b/usr.sbin/sysinstall/tcpip.c
@@ -103,7 +103,7 @@ static Layout layout[] = {
     { 19, 35, 0, 0,
       "CANCEL", "Select this if you wish to cancel this screen",
       &cancelbutton, BUTTONOBJ, NULL },
-    { NULL },
+    { 0 },
 };
 
 #define _validByte(b) ((b) >= 0 && (b) <= 255)
diff --git a/usr.sbin/sysinstall/user.c b/usr.sbin/sysinstall/user.c
index 1b0b845ae9e8..ecee440fe788 100644
--- a/usr.sbin/sysinstall/user.c
+++ b/usr.sbin/sysinstall/user.c
@@ -102,7 +102,7 @@ static Layout groupLayout[] = {
     { 18, 35, 0, 0,
       "CANCEL", "Select this if you wish to cancel this screen",
       &cancelbutton, BUTTONOBJ, NULL },
-    { NULL },
+    { 0 },
 };
 
 /* The user configuration menu. */
@@ -147,7 +147,7 @@ static Layout userLayout[] = {
     { 18, 35, 0, 0,
       "CANCEL", "Select this if you wish to cancel this screen",
       &cancelbutton, BUTTONOBJ, NULL },
-    { NULL },
+    { 0 },
 };
 
 /* whine */
diff --git a/usr.sbin/sysinstall/variable.c b/usr.sbin/sysinstall/variable.c
index e1328629d8a1..e86104fd100a 100644
--- a/usr.sbin/sysinstall/variable.c
+++ b/usr.sbin/sysinstall/variable.c
@@ -205,7 +205,7 @@ variable_check2(char *data)
 	    *cp3 = '\0';
         cp2 = variable_get(tmp);
         if (cp2 != NULL) {
-	    if (*cp == NULL)
+	    if (*cp == '\0')
 		return 2;
 	    else
 		return strcmp(cp, cp2) == 0 ? 1 : 0;