diff --git a/extensions/libipt_SET.c b/extensions/libipt_SET.c
index 378b77e..62d959f 100644
--- a/extensions/libipt_SET.c
+++ b/extensions/libipt_SET.c
@@ -34,9 +34,9 @@
 }
 
 static const struct option SET_opts[] = {
-	{"add-set",   1, 0, '1'},
-	{"del-set",   1, 0, '2'},
-	{0}
+	{"add-set",   1, NULL, '1'},
+	{"del-set",   1, NULL, '2'},
+	{ }
 };
 
 /* Initialize the target. */
diff --git a/extensions/libipt_set.c b/extensions/libipt_set.c
index dcb74df..759bca3 100644
--- a/extensions/libipt_set.c
+++ b/extensions/libipt_set.c
@@ -32,8 +32,8 @@
 }
 
 static const struct option set_opts[] = {
-	{"set", 1, 0, '1'},
-	{0}
+	{"set", 1, NULL, '1'},
+	{ }
 };
 
 /* Initialize the match. */
diff --git a/extensions/libxt_CONNSECMARK.c b/extensions/libxt_CONNSECMARK.c
index 579ea4c..2c425cb 100644
--- a/extensions/libxt_CONNSECMARK.c
+++ b/extensions/libxt_CONNSECMARK.c
@@ -23,8 +23,8 @@
 }
 
 static const struct option CONNSECMARK_opts[] = {
-	{ "save", 0, 0, '1' },
-	{ "restore", 0, 0, '2' },
+	{ "save", 0, NULL, '1' },
+	{ "restore", 0, NULL, '2' },
 	{ .name = NULL }
 };
 
diff --git a/extensions/libxt_SECMARK.c b/extensions/libxt_SECMARK.c
index feee0e4..7d3dbfa 100644
--- a/extensions/libxt_SECMARK.c
+++ b/extensions/libxt_SECMARK.c
@@ -22,7 +22,7 @@
 }
 
 static const struct option SECMARK_opts[] = {
-	{ "selctx", 1, 0, '1' },
+	{ "selctx", 1, NULL, '1' },
 	{ .name = NULL }
 };
 
diff --git a/extensions/libxt_quota.c b/extensions/libxt_quota.c
index a642aa4..8e178fe 100644
--- a/extensions/libxt_quota.c
+++ b/extensions/libxt_quota.c
@@ -77,7 +77,7 @@
 	return 1;
 }
 
-struct xtables_match quota_match = {
+static struct xtables_match quota_match = {
 	.family		= AF_UNSPEC,
 	.name		= "quota",
 	.version	= XTABLES_VERSION,
diff --git a/ip6tables-restore.c b/ip6tables-restore.c
index 9f6108a..cd6dd03 100644
--- a/ip6tables-restore.c
+++ b/ip6tables-restore.c
@@ -124,7 +124,7 @@
 	int c;
 	char curtable[IP6T_TABLE_MAXNAMELEN + 1];
 	FILE *in;
-	const char *modprobe = 0;
+	const char *modprobe = NULL;
 	int in_table = 0, testing = 0;
 
 	program_name = "ip6tables-restore";
diff --git a/iptables-restore.c b/iptables-restore.c
index 879683c..4b199d9 100644
--- a/iptables-restore.c
+++ b/iptables-restore.c
@@ -124,9 +124,9 @@
 	int c;
 	char curtable[IPT_TABLE_MAXNAMELEN + 1];
 	FILE *in;
-	const char *modprobe = 0;
+	const char *modprobe = NULL;
 	int in_table = 0, testing = 0;
-	const char *tablename = 0;
+	const char *tablename = NULL;
 
 	program_name = "iptables-restore";
 	program_version = XTABLES_VERSION;