diff --git a/c/reg_test/expected/out b/c/reg_test/expected/out
index 31578b05c..f9e636dc0 100644
--- a/c/reg_test/expected/out
+++ b/c/reg_test/expected/out
@@ -7501,6 +7501,70 @@ mlr --opprint filter isnotnull($z) ./reg_test/input/nullvals.dkvp
 
 mlr --opprint filter isnotnull($nosuch) ./reg_test/input/nullvals.dkvp
 
+mlr --opprint put $f=isnull($x) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - false
+b 3 4 - false
+b 5 - - false
+b - 6 - true
+b - - - true
+
+mlr --opprint put $f=isnull($y) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - false
+b 3 4 - false
+b 5 - - true
+b - 6 - false
+b - - - true
+
+mlr --opprint put $f=isnull($z) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - true
+b 3 4 - true
+b 5 - - true
+b - 6 - true
+b - - - true
+
+mlr --opprint put $f=isnull($nosuch) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - -
+b 3 4 - -
+b 5 - - -
+b - 6 - -
+b - - - -
+
+mlr --opprint put $f=isnotnull($x) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - true
+b 3 4 - true
+b 5 - - true
+b - 6 - false
+b - - - false
+
+mlr --opprint put $f=isnotnull($y) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - true
+b 3 4 - true
+b 5 - - false
+b - 6 - true
+b - - - false
+
+mlr --opprint put $f=isnotnull($z) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - false
+b 3 4 - false
+b 5 - - false
+b - 6 - false
+b - - - false
+
+mlr --opprint put $f=isnotnull($nosuch) ./reg_test/input/nullvals.dkvp
+a x y z f
+b 1 2 - -
+b 3 4 - -
+b 5 - - -
+b - 6 - -
+b - - - -
+
 
 ================================================================
 DSL TYPE-INFERENCE
diff --git a/c/reg_test/run b/c/reg_test/run
index 45e673715..33fe40619 100755
--- a/c/reg_test/run
+++ b/c/reg_test/run
@@ -699,6 +699,15 @@ run_mlr --opprint filter 'isnotnull($y)'      $indir/nullvals.dkvp
 run_mlr --opprint filter 'isnotnull($z)'      $indir/nullvals.dkvp
 run_mlr --opprint filter 'isnotnull($nosuch)' $indir/nullvals.dkvp
 
+run_mlr --opprint put '$f=isnull($x)'         $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnull($y)'         $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnull($z)'         $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnull($nosuch)'    $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnotnull($x)'      $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnotnull($y)'      $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnotnull($z)'      $indir/nullvals.dkvp
+run_mlr --opprint put '$f=isnotnull($nosuch)' $indir/nullvals.dkvp
+
 # ----------------------------------------------------------------
 announce DSL TYPE-INFERENCE