diff --git a/partiql-planner/src/main/kotlin/org/partiql/planner/internal/PartiQLHeader.kt b/partiql-planner/src/main/kotlin/org/partiql/planner/internal/PartiQLHeader.kt
index 38d851d94a..24e5e22bff 100644
--- a/partiql-planner/src/main/kotlin/org/partiql/planner/internal/PartiQLHeader.kt
+++ b/partiql-planner/src/main/kotlin/org/partiql/planner/internal/PartiQLHeader.kt
@@ -411,8 +411,8 @@ internal object PartiQLHeader : Header() {
                 parameters = listOf(
                     FunctionParameter("value", ANY)
                 ),
-                isNullCall = false, // TODO: Should this be true?
-                isNullable = false
+                isNullable = false,
+                isNullCall = false,
             )
         }
 
@@ -427,7 +427,7 @@ internal object PartiQLHeader : Header() {
                 FunctionParameter("type_parameter_1", INT32),
                 FunctionParameter("value", ANY)
             ),
-            isNullable = false, // TODO: Should this be true?
+            isNullable = false,
             isNullCall = false
         )
     }
@@ -455,8 +455,8 @@ internal object PartiQLHeader : Header() {
                 FunctionParameter("type_parameter_2", INT32),
                 FunctionParameter("value", ANY) // TODO: Decide if we need to further segment this
             ),
-            isNullCall = false,
-            isNullable = false
+            isNullable = false,
+            isNullCall = false
         )
     }
 
diff --git a/partiql-planner/src/test/kotlin/org/partiql/planner/internal/typer/PlanTyperTestsPorted.kt b/partiql-planner/src/test/kotlin/org/partiql/planner/internal/typer/PlanTyperTestsPorted.kt
index f88852c3c0..0f7b548c92 100644
--- a/partiql-planner/src/test/kotlin/org/partiql/planner/internal/typer/PlanTyperTestsPorted.kt
+++ b/partiql-planner/src/test/kotlin/org/partiql/planner/internal/typer/PlanTyperTestsPorted.kt
@@ -388,6 +388,66 @@ class PlanTyperTestsPorted {
             ),
         )
 
+        @JvmStatic
+        fun isTypeCases() = listOf(
+            SuccessTestCase(
+                name = "IS BOOL",
+                key = key("is-type-00"),
+                catalog = "pql",
+                catalogPath = listOf("main"),
+                expected = StaticType.BOOL
+            ),
+            SuccessTestCase(
+                name = "IS INT",
+                key = key("is-type-01"),
+                catalog = "pql",
+                catalogPath = listOf("main"),
+                expected = StaticType.BOOL
+            ),
+            SuccessTestCase(
+                name = "IS STRING",
+                key = key("is-type-02"),
+                catalog = "pql",
+                catalogPath = listOf("main"),
+                expected = StaticType.BOOL
+            ),
+            SuccessTestCase(
+                name = "IS NULL",
+                key = key("is-type-03"),
+                catalog = "pql",
+                expected = StaticType.BOOL,
+            ),
+            SuccessTestCase(
+                name = "MISSING IS NULL",
+                key = key("is-type-04"),
+                catalog = "pql",
+                expected = StaticType.BOOL,
+            ),
+            SuccessTestCase(
+                name = "NULL IS NULL",
+                key = key("is-type-05"),
+                catalog = "pql",
+                expected = StaticType.BOOL,
+            ),
+            SuccessTestCase(
+                name = "MISSING IS MISSING",
+                key = key("is-type-06"),
+                catalog = "pql",
+                expected = StaticType.BOOL,
+            ),
+            SuccessTestCase(
+                name = "NULL IS MISSING",
+                key = key("is-type-07"),
+                catalog = "pql",
+                expected = StaticType.BOOL,
+            ),
+            ErrorTestCase(
+                name = "ERROR always MISSING",
+                key = key("is-type-08"),
+                catalog = "pql",
+            ),
+        )
+
         @JvmStatic
         fun sessionVariables() = listOf(
             SuccessTestCase(
@@ -536,7 +596,10 @@ class PlanTyperTestsPorted {
                 problemHandler = assertProblemExists {
                     Problem(
                         UNKNOWN_PROBLEM_LOCATION,
-                        PlanningProblemDetails.UnknownFunction("bitwise_and", listOf(StaticType.INT4, StaticType.STRING))
+                        PlanningProblemDetails.UnknownFunction(
+                            "bitwise_and",
+                            listOf(StaticType.INT4, StaticType.STRING)
+                        )
                     )
                 }
             ),
@@ -2972,6 +3035,11 @@ class PlanTyperTestsPorted {
     @Execution(ExecutionMode.CONCURRENT)
     fun testPivot(tc: TestCase) = runTest(tc)
 
+    @ParameterizedTest
+    @MethodSource("isTypeCases")
+    @Execution(ExecutionMode.CONCURRENT)
+    fun testIsType(tc: TestCase) = runTest(tc)
+
     // --------- Finish Parameterized Tests ------
 
     //
@@ -2980,7 +3048,7 @@ class PlanTyperTestsPorted {
     private fun infer(
         query: String,
         session: PartiQLPlanner.Session,
-        problemCollector: ProblemCollector
+        problemCollector: ProblemCollector,
     ): PartiQLPlan {
         val ast = parser.parse(query).root
         return planner.plan(ast, session, problemCollector).plan
diff --git a/partiql-planner/src/testFixtures/resources/inputs/schema_inferencer/is_type.sql b/partiql-planner/src/testFixtures/resources/inputs/schema_inferencer/is_type.sql
new file mode 100644
index 0000000000..7a8da457f5
--- /dev/null
+++ b/partiql-planner/src/testFixtures/resources/inputs/schema_inferencer/is_type.sql
@@ -0,0 +1,27 @@
+--#[is-type-00]
+false IS BOOL;
+
+--#[is-type-01]
+item.i_class_id IS INT;
+
+--#[is-type-02]
+item.i_brand IS STRING;
+
+--#[is-type-03]
+1 IS NULL;
+
+--#[is-type-04]
+MISSING IS NULL;
+
+--#[is-type-05]
+NULL IS NULL;
+
+--#[is-type-06]
+MISSING IS MISSING;
+
+--#[is-type-07]
+NULL IS MISSING;
+
+--#[is-type-08]
+-- ERROR! always MISSING
+MISSING IS BOOL;