diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSetBaseOperatorConversion.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSetBaseOperatorConversion.java
index 0afad6cbe6b1..62c686cd2b2a 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSetBaseOperatorConversion.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSetBaseOperatorConversion.java
@@ -63,6 +63,8 @@ public DruidExpression toDruidExpression(
       RexNode rexNode
   )
   {
+    plannerContext.setPlanningError("%s can only be used on aggregates. " +
+        "It cannot be used directly on a column or on a scalar expression.", getFunctionName());
     return null;
   }
 
diff --git a/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSqlAggregatorTest.java b/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSqlAggregatorTest.java
index ac7ae090558f..f5a23178dd02 100644
--- a/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSqlAggregatorTest.java
+++ b/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/theta/sql/ThetaSketchSqlAggregatorTest.java
@@ -1014,4 +1014,12 @@ public void testGroupByAggregatorDefaultValuesFinalizeOuterSketches()
         ImmutableList.of(new Object[]{"a", 0L, 0L, "0.0", "0.0"})
     );
   }
+
+  @Test
+  public void testThetaSketchIntersectOnScalarExpression()
+  {
+    assertQueryIsUnplannable("SELECT THETA_SKETCH_INTERSECT(NULL, NULL) FROM foo",
+        "Possible error: THETA_SKETCH_INTERSECT can only be used on aggregates. " +
+            "It cannot be used directly on a column or on a scalar expression.");
+  }
 }