diff --git a/usr.bin/at/at.c b/usr.bin/at/at.c
index 3eb3e740f7e4..71d8e607f9c9 100644
--- a/usr.bin/at/at.c
+++ b/usr.bin/at/at.c
@@ -184,7 +184,7 @@ nextjob()
     long jobno;
     FILE *fid;
 
-    if ((fid = fopen(ATJOB_DIR ".SEQ", "r+")) != (FILE*)0) {
+    if ((fid = fopen(ATJOB_DIR ".SEQ", "r+")) != NULL) {
 	if (fscanf(fid, "%5lx", &jobno) == 1) {
 	    rewind(fid);
 	    jobno = (1+jobno) % 0xfffff;	/* 2^20 jobs enough? */
@@ -195,7 +195,7 @@ nextjob()
 	fclose(fid);
 	return jobno;
     }
-    else if ((fid = fopen(ATJOB_DIR ".SEQ", "w")) != (FILE*)0) {
+    else if ((fid = fopen(ATJOB_DIR ".SEQ", "w")) != NULL) {
 	fprintf(fid, "%05lx\n", jobno = 1);
 	fclose(fid);
 	return 1;
diff --git a/usr.bin/login/login_fbtab.c b/usr.bin/login/login_fbtab.c
index 684cf6131696..f6111a1cd352 100644
--- a/usr.bin/login/login_fbtab.c
+++ b/usr.bin/login/login_fbtab.c
@@ -93,8 +93,8 @@ gid_t   gid;
     int     prot;
     const char *table;
 
-    if ((fp = fopen(table = _PATH_FBTAB, "r")) == 0
-    && (fp = fopen(table = _PATH_LOGINDEVPERM, "r")) == 0)
+    if ((fp = fopen(table = _PATH_FBTAB, "r")) == NULL
+    && (fp = fopen(table = _PATH_LOGINDEVPERM, "r")) == NULL)
 	return;
 
     while (fgets(buf, sizeof(buf), fp)) {
diff --git a/usr.bin/m4/gnum4.c b/usr.bin/m4/gnum4.c
index 8940bb820f77..f4cfa7786017 100644
--- a/usr.bin/m4/gnum4.c
+++ b/usr.bin/m4/gnum4.c
@@ -133,7 +133,7 @@ dopath(struct input_file *i, const char *filename)
 
 	for (pe = first; pe; pe = pe->next) {
 		snprintf(path, sizeof(path), "%s/%s", pe->name, filename);
-		if ((f = fopen(path, "r")) != 0) {
+		if ((f = fopen(path, "r")) != NULL) {
 			set_input(i, f, path);
 			return i;
 		}
diff --git a/usr.bin/mklocale/yacc.y b/usr.bin/mklocale/yacc.y
index 84149f019480..899b186d93c4 100644
--- a/usr.bin/mklocale/yacc.y
+++ b/usr.bin/mklocale/yacc.y
@@ -234,7 +234,7 @@ main(int ac, char *av[])
 	    break;
 	case 'o':
 	    locale_file = optarg;
-	    if ((fp = fopen(locale_file, "w")) == 0)
+	    if ((fp = fopen(locale_file, "w")) == NULL)
 		err(1, "%s", locale_file);
 	    atexit(cleanout);
 	    break;