diff --git a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/grouping/Categorize.java b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/grouping/Categorize.java
index e2c04ecb15b59..83ea11d38b161 100644
--- a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/grouping/Categorize.java
+++ b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/grouping/Categorize.java
@@ -13,6 +13,7 @@
 import org.elasticsearch.compute.operator.EvalOperator.ExpressionEvaluator;
 import org.elasticsearch.xpack.esql.capabilities.Validatable;
 import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.expression.Nullability;
 import org.elasticsearch.xpack.esql.core.tree.NodeInfo;
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
@@ -92,6 +93,11 @@ public boolean foldable() {
         return false;
     }
 
+    @Override
+    public Nullability nullable() {
+        return Nullability.FALSE;
+    }
+
     @Override
     public ExpressionEvaluator.Factory toEvaluator(ToEvaluator toEvaluator) {
         throw new UnsupportedOperationException("CATEGORIZE is only evaluated during aggregations");
diff --git a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/FoldNull.java b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/FoldNull.java
index 638fa1b8db456..0f08cd66444a3 100644
--- a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/FoldNull.java
+++ b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/FoldNull.java
@@ -13,7 +13,6 @@
 import org.elasticsearch.xpack.esql.core.expression.Literal;
 import org.elasticsearch.xpack.esql.core.expression.Nullability;
 import org.elasticsearch.xpack.esql.expression.function.aggregate.AggregateFunction;
-import org.elasticsearch.xpack.esql.expression.function.grouping.Categorize;
 import org.elasticsearch.xpack.esql.expression.predicate.operator.comparison.In;
 
 public class FoldNull extends OptimizerRules.OptimizerExpressionRule<Expression> {
@@ -43,7 +42,6 @@ public Expression rule(Expression e) {
             }
         } else if (e instanceof Alias == false
             && e.nullable() == Nullability.TRUE
-            && e instanceof Categorize == false
             && Expressions.anyMatch(e.children(), Expressions::isNull)) {
                 return Literal.of(e, null);
             }