diff --git a/scripts-available/CDB_CartodbfyTable.sql b/scripts-available/CDB_CartodbfyTable.sql
index 2e44e9a..84a6d51 100644
--- a/scripts-available/CDB_CartodbfyTable.sql
+++ b/scripts-available/CDB_CartodbfyTable.sql
@@ -362,7 +362,7 @@ $$ LANGUAGE PLPGSQL;
 --     As before, this drops all the metadata and geom sync triggers
 --
 -- (2) _CDB_Has_Usable_Primary_ID()
---     Returns TRUE if it can find a unique integer primary key named
+--     Returns TRUE if it can find a unique and not null integer primary key named
 --    'cartodb_id' or can rename an existing key.
 --     Returns FALSE otherwise.
 --
@@ -551,7 +551,7 @@ BEGIN
         RAISE DEBUG 'CDB(_CDB_Has_Usable_Primary_ID): %', Format('found good ''%s''', const.pkey);
         RETURN true;
 
-      -- Check and see if the column values are unique, 
+      -- Check and see if the column values are unique and not null, 
       -- if they are, we can use this column...
       ELSE
 
@@ -559,13 +559,17 @@ BEGIN
         useable_key := true;
       
         BEGIN
-          sql := Format('ALTER TABLE %s ADD CONSTRAINT %s_unique UNIQUE (%s)', reloid::text, const.pkey, const.pkey);
+          sql := Format('ALTER TABLE %s ADD CONSTRAINT %s_pk PRIMARY KEY (%s)', reloid::text, const.pkey, const.pkey);
           RAISE DEBUG 'CDB(_CDB_Has_Usable_Primary_ID): %', sql;
           EXECUTE sql;
           EXCEPTION      
           -- Failed unique check...
           WHEN unique_violation THEN
-            RAISE NOTICE 'CDB(_CDB_Has_Usable_Primary_ID): %', Format('column %s is not unique', const.pkey);
+            RAISE DEBUG 'CDB(_CDB_Has_Usable_Primary_ID): %', Format('column %s is not unique', const.pkey);
+            useable_key := false;
+          -- Failed not null check...
+          WHEN not_null_violation THEN
+            RAISE DEBUG 'CDB(_CDB_Has_Usable_Primary_ID): %', Format('column %s contains nulls', const.pkey);
             useable_key := false;
           -- Other fatal error
           WHEN others THEN
@@ -574,7 +578,7 @@ BEGIN
   
         -- Clean up test constraint
         IF useable_key THEN
-          PERFORM _CDB_SQL(Format('ALTER TABLE %s DROP CONSTRAINT %s_unique', reloid::text, const.pkey));
+          PERFORM _CDB_SQL(Format('ALTER TABLE %s DROP CONSTRAINT %s_pk', reloid::text, const.pkey));
 
         -- Move non-unique column out of the way
         ELSE
diff --git a/test/CDB_CartodbfyTableTest.sql b/test/CDB_CartodbfyTableTest.sql
index b35540b..dc4bab7 100644
--- a/test/CDB_CartodbfyTableTest.sql
+++ b/test/CDB_CartodbfyTableTest.sql
@@ -250,7 +250,7 @@ INSERT INTO existing_cartodb_id (cartodb_id, description) VALUES
        (20, 'b'),
        (30, 'c');
 SELECT CDB_CartodbfyTableCheck('existing_cartodb_id', 'Existing cartodb_id values are respected #138');
-SELECT * from existing_cartodb_id;
+SELECT cartodb_id,the_geom,the_geom_webmercator,description,name from existing_cartodb_id;
 DROP TABLE existing_cartodb_id;
 
 -- Table with both the_geom and wkb_geometry
@@ -281,6 +281,44 @@ INSERT INTO many_colliding_columns VALUES (
 SELECT CDB_CartodbfyTableCheck('many_colliding_columns', 'Many colliding columns #141');
 DROP TABLE many_colliding_columns;
 
+-- Table with null cartodb_id
+CREATE TABLE test (
+  cartodb_id integer
+);
+INSERT INTO test VALUES
+  (1), 
+  (2), 
+  (NULL), 
+  (3);
+SELECT CDB_CartodbfyTableCheck('test', 'Table with null cartodb_id #148');
+SELECT cartodb_id, cartodb_id_1 from test;
+DROP TABLE test;
+
+-- Table with non unique cartodb_id
+CREATE TABLE test (
+  cartodb_id integer
+);
+INSERT INTO test VALUES
+  (1), 
+  (2), 
+  (2);
+SELECT CDB_CartodbfyTableCheck('test', 'Table with non unique cartodb_id #148');
+SELECT cartodb_id, cartodb_id_1 from test;
+DROP TABLE test;
+
+-- Table with non unique and null cartodb_id
+CREATE TABLE test (
+  cartodb_id integer
+);
+INSERT INTO test VALUES
+  (1),
+  (2),
+  (NULL),
+  (2);
+SELECT CDB_CartodbfyTableCheck('test', 'Table with non unique and null cartodb_id #148');
+SELECT cartodb_id, cartodb_id_1 from test;
+DROP TABLE test;
+
 
 -- TODO: table with existing custom-triggered the_geom
 
diff --git a/test/CDB_CartodbfyTableTest_expect b/test/CDB_CartodbfyTableTest_expect
index 6287c3f..6103dc8 100644
--- a/test/CDB_CartodbfyTableTest_expect
+++ b/test/CDB_CartodbfyTableTest_expect
@@ -79,5 +79,28 @@ CREATE TABLE
 INSERT 0 1
 Many colliding columns #141 cartodbfied fine
 DROP TABLE
+CREATE TABLE
+INSERT 0 4
+Table with null cartodb_id #148 cartodbfied fine
+1|1
+2|2
+3|
+4|3
+DROP TABLE
+CREATE TABLE
+INSERT 0 3
+Table with non unique cartodb_id #148 cartodbfied fine
+1|1
+2|2
+3|2
+DROP TABLE
+CREATE TABLE
+INSERT 0 4
+Table with non unique and null cartodb_id #148 cartodbfied fine
+1|1
+2|2
+3|
+4|2
+DROP TABLE
 DROP FUNCTION
 DROP FUNCTION