diff --git a/README.md b/README.md
index 0439f98..e8df1a6 100644
--- a/README.md
+++ b/README.md
@@ -58,8 +58,8 @@ SQL = "SELECT title FROM posts WHERE lang = $1 ORDER BY date DESC OFFSET 10 ROWS
 QueryDSL = [select('posts.title','author.name'), from(posts), join(author), on('author.author_id' = 'posts.author_id')]
 SQL = "SELECT posts.title,author.name FROM posts INNER JOIN author ON author.author_id = posts.author_id"
 
-QueryDSL = [select(title), from(posts), where((lang = "es";lang='NULL')), order_by(desc(date), asc(title))]
-SQL = "SELECT title FROM posts WHERE (lang = $1) OR (lang = NULL) ORDER BY date DESC,title ASC"
+QueryDSL = [select(title), from(posts), where((lang = "es";is_null(lang))), order_by(desc(date), asc(title))]
+SQL = "SELECT title FROM posts WHERE (lang = $1) OR (lang IS NULL) ORDER BY date DESC,title ASC"
 
 QueryDSL = [insert_into(test_table, [name]), values("test")]
 SQL = "INSERT INTO test_table (name) VALUES ($1)"
diff --git a/messages.pl b/messages.pl
index 5ee47e9..1606f3d 100644
--- a/messages.pl
+++ b/messages.pl
@@ -101,7 +101,7 @@
     length(Params, NumberParams),
     int16(NumberParams, Bytes4),
     bind_message_params_bytes(Params, [], Bytes5),
-    append([Bytes1, Bytes2, Bytes3, Bytes4, Bytes5], PreBytes),
+    append([Bytes1, Bytes2, Bytes3, Bytes4, Bytes5, Bytes3], PreBytes),
     length(PreBytes, L),
     RealLength is L + 4,
     int32(RealLength, Bytes0),
@@ -109,9 +109,7 @@
 
 bind_message_params_bytes([], B, B).
 bind_message_params_bytes([null|Params], Bytes0, Bytes) :-
-    int32(-1, B1),
-    int16(0, B2),
-    append([B1, B2], B),
+    int32(-1, B),
     append(Bytes0, B, Bytes1),
     bind_message_params_bytes(Params, Bytes1, Bytes).
 
@@ -119,8 +117,7 @@
     chars_utf8bytes(Param, B2),
     length(B2, L),
     int32(L, B1),
-    int16(0, B3),
-    append([B1, B2, B3], B),
+     append([B1, B2], B),
     append(Bytes0, B, Bytes1),
     bind_message_params_bytes(Params, Bytes1, Bytes).
 
diff --git a/sql_query.pl b/sql_query.pl
index afb49f3..143a492 100644
--- a/sql_query.pl
+++ b/sql_query.pl
@@ -143,6 +143,15 @@
     sql_cond(B, Vars1, Vars),
     ")".
 
+sql_cond((\+ A), Vars0, Vars) -->
+    "NOT (",
+    sql_cond(A, Vars0, Vars),
+    ")".
+
+sql_cond(is_null(A), Vars0, Vars) -->
+    { sql_var(A, VarA, Vars0, Vars) },    
+    format_("~w IS NULL", [VarA]).
+
 sql_cond(A = B, Vars0, Vars) -->
     { sql_var(A, VarA, Vars0, Vars1) },
     { sql_var(B, VarB, Vars1, Vars) },
diff --git a/tests.lgt b/tests.lgt
index 09b1499..6dd0803 100644
--- a/tests.lgt
+++ b/tests.lgt
@@ -105,8 +105,8 @@
 
     test(sql_query_or) :-
         sql_query:sql_query(
-	    [select(title), from(posts), where((lang = "es";lang='NULL')), order_by(desc(date), asc(title))],
-	    "SELECT title FROM posts WHERE (lang = $1) OR (lang = NULL) ORDER BY date DESC,title ASC",
+	    [select(title), from(posts), where((lang = "es";is_null(lang))), order_by(desc(date), asc(title))],
+	    "SELECT title FROM posts WHERE (lang = $1) OR (lang IS NULL) ORDER BY date DESC,title ASC",
 	    [1-"es"]
 	).
 
@@ -156,7 +156,19 @@
 	postgresql:sql(Connection, [select(id, name), from(test_table), where(name = "test")], Rows2),
 	Rows2 = data([]).
 
-
+    test(sql_query_2) :-
+        postgresql:connect("postgres", "postgres", '127.0.0.1', 5432, "postgres", Connection),
+	postgresql:query(Connection, "DROP TABLE IF EXISTS famous", ok),		
+	postgresql:query(Connection, "DROP TABLE IF EXISTS country", ok),
+	postgresql:query(Connection, "CREATE TABLE country (iso_code varchar(2) PRIMARY KEY, name text)", ok),
+	postgresql:query(Connection, "CREATE TABLE famous (id serial PRIMARY KEY, name text, country varchar(2) REFERENCES country(iso_code), year int)", ok),
+	postgresql:sql(Connection, [insert_into(country, [iso_code, name]), values("ES", "España")], data([])),
+	postgresql:sql(Connection, [insert_into(country, [iso_code, name]), values("PT", "Portugal")], data([])),
+	postgresql:sql(Connection, [insert_into(famous, [name, country, year]), values("Miguel de Cervantes", "ES", 1547)], data([])),
+	postgresql:sql(Connection, [insert_into(famous, [name, country, year]), values("Magallanes", "PT", 1480)], data([])),
+	postgresql:sql(Connection, [insert_into(famous, [name, country, year]), values("Picasso", "ES", 1881)], data([])),
+	postgresql:sql(Connection, [select('famous.name','country.name'),from(famous),join(country),on('famous.country' = 'country.iso_code'),where((year > 1500,year < 2000)),order_by(asc(year))], Result),
+	Result = data([["Miguel de Cervantes", "España"], ["Picasso", "España"]]).
 
 
 :- end_object.
\ No newline at end of file