diff --git a/bin/pt-query-advisor b/bin/pt-query-advisor
index 85bc76d8..5f26b3fc 100755
--- a/bin/pt-query-advisor
+++ b/bin/pt-query-advisor
@@ -4056,8 +4056,8 @@ sub determine_table_for_column {
 
 sub _looks_like_column {
    my $col = shift;
-   return if $col eq '*' || $col eq 'NULL';
-   return if $col =~ /\A(?:\b[0-9]+\b|[^(]+\(|\@{1,2}.+)/;
+   return if $col eq '*' || uc($col) eq 'NULL';
+   return if $col =~ /\A(?:\b[0-9]+\b|\@{1,2}.+)/;
    return $col;
 }
 
diff --git a/lib/QueryAdvisorRules.pm b/lib/QueryAdvisorRules.pm
index 119eb1d0..3d4cddc1 100644
--- a/lib/QueryAdvisorRules.pm
+++ b/lib/QueryAdvisorRules.pm
@@ -667,8 +667,8 @@ sub determine_table_for_column {
 sub _looks_like_column {
    my $col = shift;
    # NULL, numbers, variables and functions are definitely not columns
-   return if $col eq '*' || $col eq 'NULL';
-   return if $col =~ /\A(?:\b[0-9]+\b|[^(]+\(|\@{1,2}.+)/;
+   return if $col eq '*' || uc($col) eq 'NULL';
+   return if $col =~ /\A(?:\b[0-9]+\b|\@{1,2}.+)/;
    return $col;
 }
 
diff --git a/t/lib/QueryAdvisorRules.t b/t/lib/QueryAdvisorRules.t
index 2733d390..3a8f6ca5 100644
--- a/t/lib/QueryAdvisorRules.t
+++ b/t/lib/QueryAdvisorRules.t
@@ -468,7 +468,7 @@ my @cases = (
    },
    {
       name   => 'Bug 937234: wrong RES.001',
-      query  => q{select NULL, 1, COUNT(*), @@time_zone, foo as field2 from t1 group by field2},
+      query  => q{select NULL, null, 1, COUNT(*), @@time_zone, foo as field2 from t1 group by field2},
       advice => [qw(CLA.001)],
    },
    {