diff --git a/src/iceberg/partition_spec.cc b/src/iceberg/partition_spec.cc
index 90be924b2..29ff046c1 100644
--- a/src/iceberg/partition_spec.cc
+++ b/src/iceberg/partition_spec.cc
@@ -82,13 +82,9 @@ Result<std::unique_ptr<StructType>> PartitionSpec::PartitionType(
   for (const auto& partition_field : fields_) {
     ICEBERG_ASSIGN_OR_RAISE(auto source_field,
                             schema.FindFieldById(partition_field.source_id()));
-    std::shared_ptr<Type> result_type;
-    if (source_field.has_value()) {
-      auto source_field_type = source_field.value().get().type();
-      result_type = partition_field.transform()->ResultType(std::move(source_field_type));
-    } else {
-      result_type = unknown();
-    }
+    // Fixed-result transforms retain their type after the source column is dropped.
+    auto source_type = source_field.has_value() ? source_field->get().type() : unknown();
+    auto result_type = partition_field.transform()->ResultType(source_type);
 
     partition_fields.emplace_back(partition_field.field_id(),
                                   std::string(partition_field.name()),
diff --git a/src/iceberg/test/partition_spec_test.cc b/src/iceberg/test/partition_spec_test.cc
index 9a31b065a..f7919f605 100644
--- a/src/iceberg/test/partition_spec_test.cc
+++ b/src/iceberg/test/partition_spec_test.cc
@@ -171,17 +171,23 @@ TEST(PartitionSpecTest, PartitionTypeMissingSource) {
       PartitionSpec::Make(
           1, {PartitionField(1, 1000, "dropped_identity", Transform::Identity()),
               PartitionField(3, 1001, "dropped_bucket", Transform::Bucket(16)),
-              PartitionField(2, 1002, "ts_day", Transform::Day())}));
+              PartitionField(2, 1002, "ts_day", Transform::Day()),
+              PartitionField(4, 1003, "dropped_day", Transform::Day()),
+              PartitionField(4, 1004, "dropped_year", Transform::Year())}));
 
   ICEBERG_UNWRAP_OR_FAIL(auto partition_type, spec->PartitionType(schema));
 
-  ASSERT_EQ(partition_type->fields().size(), 3U);
+  ASSERT_EQ(partition_type->fields().size(), 5U);
   EXPECT_EQ(partition_type->fields()[0],
             SchemaField::MakeOptional(1000, "dropped_identity", unknown()));
   EXPECT_EQ(partition_type->fields()[1],
-            SchemaField::MakeOptional(1001, "dropped_bucket", unknown()));
+            SchemaField::MakeOptional(1001, "dropped_bucket", int32()));
   EXPECT_EQ(partition_type->fields()[2],
             SchemaField::MakeOptional(1002, "ts_day", date()));
+  EXPECT_EQ(partition_type->fields()[3],
+            SchemaField::MakeOptional(1003, "dropped_day", date()));
+  EXPECT_EQ(partition_type->fields()[4],
+            SchemaField::MakeOptional(1004, "dropped_year", int32()));
 }
 
 TEST(PartitionSpecTest, RawPartitionTypeNoReassign) {