diff --git a/clients/tools/common.c b/clients/tools/common.c
index 14704b2350..0ee5a22b11 100644
--- a/clients/tools/common.c
+++ b/clients/tools/common.c
@@ -2631,7 +2631,7 @@ void tool_print_ctrls(
 		/* known controls */
 		for ( j = 0; tool_ctrl_response[j].oid != NULL; j++ ) {
 			if ( strcmp( tool_ctrl_response[j].oid, ctrls[i]->ldctl_oid ) == 0 ) {
-				if ( !tool_ctrl_response[j].mask & tool_type ) {
+				if ( !(tool_ctrl_response[j].mask & tool_type )) {
 					/* this control should not appear
 					 * with this tool; warning? */
 				}
diff --git a/servers/slapd/backend.c b/servers/slapd/backend.c
index f62e69e87d..d8a91bc717 100644
--- a/servers/slapd/backend.c
+++ b/servers/slapd/backend.c
@@ -1570,7 +1570,7 @@ fe_acl_group(
 					 * or if filter parsing fails.
 					 * In the latter case,
 					 * we should give up. */
-					if ( ludp->lud_filter != NULL && ludp->lud_filter != '\0') {
+					if ( ludp->lud_filter != NULL && *ludp->lud_filter != '\0') {
 						filter = str2filter_x( op, ludp->lud_filter );
 						if ( filter == NULL ) {
 							/* give up... */
diff --git a/servers/slapd/overlays/constraint.c b/servers/slapd/overlays/constraint.c
index 75efdb26a7..c9e7b1511b 100644
--- a/servers/slapd/overlays/constraint.c
+++ b/servers/slapd/overlays/constraint.c
@@ -446,7 +446,7 @@ constraint_cf_gen( ConfigArgs *c )
 						}
 
 						if ( ap.restrict_lud->lud_attrs != NULL ) {
-							if ( ap.restrict_lud->lud_attrs[0] != '\0' ) {
+							if ( ap.restrict_lud->lud_attrs[0] != NULL ) {
 								snprintf( c->cr_msg, sizeof( c->cr_msg ),
 									"%s %s: attrs not allowed in restrict URI %s\n",
 									c->argv[0], c->argv[1], arg);
diff --git a/servers/slapd/syntax.c b/servers/slapd/syntax.c
index 2176bd3bd7..308b1c9ab0 100644
--- a/servers/slapd/syntax.c
+++ b/servers/slapd/syntax.c
@@ -219,8 +219,8 @@ syn_add(
 			}
 
 			assert( (*lsei)->lsei_values != NULL );
-			if ( (*lsei)->lsei_values[0] == '\0'
-				|| (*lsei)->lsei_values[1] != '\0' )
+			if ( (*lsei)->lsei_values[0] == NULL
+				|| (*lsei)->lsei_values[1] != NULL )
 			{
 				Debug( LDAP_DEBUG_ANY, "syn_add(%s): exactly one substitute syntax must be present\n",
 					ssyn->ssyn_syn.syn_oid, 0, 0 );