diff --git a/internal/pkg/bifs/types.go b/internal/pkg/bifs/types.go
index 54fe8d3a0..59cb9c178 100644
--- a/internal/pkg/bifs/types.go
+++ b/internal/pkg/bifs/types.go
@@ -194,10 +194,10 @@ func BIF_is_notarray(input1 *mlrval.Mlrval) *mlrval.Mlrval {
 	return mlrval.FromBool(!input1.IsArray())
 }
 func BIF_is_notnull(input1 *mlrval.Mlrval) *mlrval.Mlrval {
-	return mlrval.FromBool(!input1.IsAbsent() && !input1.IsVoid())
+	return mlrval.FromBool(!input1.IsAbsent() && !input1.IsVoid() && !input1.IsNull())
 }
 func BIF_is_null(input1 *mlrval.Mlrval) *mlrval.Mlrval {
-	return mlrval.FromBool(input1.IsAbsent() || input1.IsVoid())
+	return mlrval.FromBool(input1.IsAbsent() || input1.IsVoid() || input1.IsNull())
 }
 func BIF_is_numeric(input1 *mlrval.Mlrval) *mlrval.Mlrval {
 	return mlrval.FromBool(input1.IsInt() || input1.IsFloat())
diff --git a/internal/pkg/dsl/cst/builtin_function_manager.go b/internal/pkg/dsl/cst/builtin_function_manager.go
index ce8849a8e..2b37c0286 100644
--- a/internal/pkg/dsl/cst/builtin_function_manager.go
+++ b/internal/pkg/dsl/cst/builtin_function_manager.go
@@ -1203,14 +1203,14 @@ strftime_local.`,
 		{
 			name:      "is_not_null",
 			class:     FUNC_CLASS_TYPING,
-			help:      "False if argument is null (empty or absent), true otherwise.",
+			help:      "False if argument is null (empty, absent, or JSON null), true otherwise.",
 			unaryFunc: bifs.BIF_is_notnull,
 		},
 
 		{
 			name:      "is_null",
 			class:     FUNC_CLASS_TYPING,
-			help:      "True if argument is null (empty or absent), false otherwise.",
+			help:      "True if argument is null (empty, absent, or JSON null), false otherwise.",
 			unaryFunc: bifs.BIF_is_null,
 		},
 
diff --git a/test/cases/dsl-is-predicates/0098j/cmd b/test/cases/dsl-is-predicates/0098j/cmd
new file mode 100644
index 000000000..7ecc8862a
--- /dev/null
+++ b/test/cases/dsl-is-predicates/0098j/cmd
@@ -0,0 +1 @@
+mlr --json put -f ${CASEDIR}/mlr test/input/nullvals.json
diff --git a/test/cases/dsl-is-predicates/0098j/experr b/test/cases/dsl-is-predicates/0098j/experr
new file mode 100644
index 000000000..e69de29bb
diff --git a/test/cases/dsl-is-predicates/0098j/expout b/test/cases/dsl-is-predicates/0098j/expout
new file mode 100644
index 000000000..d15d048bf
--- /dev/null
+++ b/test/cases/dsl-is-predicates/0098j/expout
@@ -0,0 +1,43 @@
+[
+{
+  "a": "r",
+  "x": 1,
+  "y": 2,
+  "z": "",
+  "f": true
+},
+{
+  "a": "s",
+  "x": 3,
+  "y": 4,
+  "z": "",
+  "f": true
+},
+{
+  "a": "t",
+  "x": 5,
+  "y": "",
+  "z": "",
+  "f": true
+},
+{
+  "a": "u",
+  "x": "",
+  "y": 6,
+  "f": true
+},
+{
+  "a": "v",
+  "x": "",
+  "y": "",
+  "z": "null",
+  "f": false
+},
+{
+  "a": "v",
+  "x": "",
+  "y": "",
+  "z": null,
+  "f": true
+}
+]
diff --git a/test/cases/dsl-is-predicates/0098j/mlr b/test/cases/dsl-is-predicates/0098j/mlr
new file mode 100644
index 000000000..64c704004
--- /dev/null
+++ b/test/cases/dsl-is-predicates/0098j/mlr
@@ -0,0 +1 @@
+$f=is_null($z)
diff --git a/test/input/nullvals.json b/test/input/nullvals.json
new file mode 100644
index 000000000..1682929f3
--- /dev/null
+++ b/test/input/nullvals.json
@@ -0,0 +1,37 @@
+[
+{
+  "a": "r",
+  "x": 1,
+  "y": 2,
+  "z": ""
+},
+{
+  "a": "s",
+  "x": 3,
+  "y": 4,
+  "z": ""
+},
+{
+  "a": "t",
+  "x": 5,
+  "y": "",
+  "z": ""
+},
+{
+  "a": "u",
+  "x": "",
+  "y": 6
+},
+{
+  "a": "v",
+  "x": "",
+  "y": "",
+  "z": "null"
+},
+{
+  "a": "v",
+  "x": "",
+  "y": "",
+  "z": null
+}
+]