diff --git a/include/sqlpp11/core/aggregate_function/avg.h b/include/sqlpp11/core/aggregate_function/avg.h
index 073bbff0..7f3c1fc8 100644
--- a/include/sqlpp11/core/aggregate_function/avg.h
+++ b/include/sqlpp11/core/aggregate_function/avg.h
@@ -83,13 +83,13 @@ namespace sqlpp
   template <typename Context, typename Flag, typename Expr>
   Context& serialize(Context& context, const avg_t<Flag, Expr>& t)
   {
-    context << "MAX(";
+    context << "AVG(";
     if (std::is_same<distinct_t, Flag>::value)
     {
       serialize(context, Flag());
       context << ' ';
     }
-    serialize_operand(context, t._expr);
+    serialize(context, t._expr);
     context << ")";
     return context;
   }
diff --git a/include/sqlpp11/core/aggregate_function/count.h b/include/sqlpp11/core/aggregate_function/count.h
index 8760aa04..32aae700 100644
--- a/include/sqlpp11/core/aggregate_function/count.h
+++ b/include/sqlpp11/core/aggregate_function/count.h
@@ -89,7 +89,7 @@ namespace sqlpp
       serialize(context, Flag());
       context << ' ';
     }
-    serialize_operand(context, t._expr);
+    serialize(context, t._expr);
     context << ")";
     return context;
   }
diff --git a/include/sqlpp11/core/aggregate_function/max.h b/include/sqlpp11/core/aggregate_function/max.h
index 612478e9..afbffc34 100644
--- a/include/sqlpp11/core/aggregate_function/max.h
+++ b/include/sqlpp11/core/aggregate_function/max.h
@@ -88,7 +88,7 @@ namespace sqlpp
       serialize(context, Flag());
       context << ' ';
     }
-    serialize_operand(context, t._expr);
+    serialize(context, t._expr);
     context << ")";
     return context;
   }
diff --git a/include/sqlpp11/core/aggregate_function/min.h b/include/sqlpp11/core/aggregate_function/min.h
index 8c154451..6b0de98a 100644
--- a/include/sqlpp11/core/aggregate_function/min.h
+++ b/include/sqlpp11/core/aggregate_function/min.h
@@ -88,7 +88,7 @@ namespace sqlpp
       serialize(context, Flag());
       context << ' ';
     }
-    serialize_operand(context, t._expr);
+    serialize(context, t._expr);
     context << ")";
     return context;
   }
diff --git a/include/sqlpp11/core/aggregate_function/sum.h b/include/sqlpp11/core/aggregate_function/sum.h
index 52d4cc9a..ca806f7e 100644
--- a/include/sqlpp11/core/aggregate_function/sum.h
+++ b/include/sqlpp11/core/aggregate_function/sum.h
@@ -90,7 +90,7 @@ namespace sqlpp
       serialize(context, Flag());
       context << ' ';
     }
-    serialize_operand(context, t._expr);
+    serialize(context, t._expr);
     context << ")";
     return context;
   }
diff --git a/tests/core/serialize/CMakeLists.txt b/tests/core/serialize/CMakeLists.txt
index 4ba89a4f..13ce3eae 100644
--- a/tests/core/serialize/CMakeLists.txt
+++ b/tests/core/serialize/CMakeLists.txt
@@ -23,9 +23,7 @@
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 set(test_files
-    Avg.cpp
     Blob.cpp
-    Count.cpp
     CustomQuery.cpp
     DynamicWhere.cpp
     Float.cpp
@@ -35,15 +33,11 @@ set(test_files
     IsNotNull.cpp
     IsNull.cpp
     Lower.cpp
-    Max.cpp
-    Min.cpp
-    Over.cpp
     Parameter.cpp
     ParameterizedVerbatim.cpp
     SelectAs.cpp
     SelectColumns.cpp
     SelectFlags.cpp
-    Sum.cpp
     TableAlias.cpp
     Trim.cpp
     Upper.cpp
@@ -61,4 +55,5 @@ foreach(test_file IN LISTS test_files)
     )
 endforeach()
 
+add_subdirectory(aggregate_function)
 add_subdirectory(operator)
diff --git a/tests/core/serialize/aggregate_function/CMakeLists.txt b/tests/core/serialize/aggregate_function/CMakeLists.txt
new file mode 100644
index 00000000..85297c18
--- /dev/null
+++ b/tests/core/serialize/aggregate_function/CMakeLists.txt
@@ -0,0 +1,38 @@
+# Copyright (c) 2024, Roland Bock
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+#   Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+#   Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+function(create_test name)
+    set(target sqlpp11_core_serialize_aggregate_function_${name})
+    add_executable(${target} ${name}.cpp)
+    target_link_libraries(${target} PRIVATE sqlpp11::sqlpp11 sqlpp11_testing)
+    add_test(NAME ${target} COMMAND ${target})
+endfunction()
+
+create_test(avg)
+create_test(count)
+create_test(max)
+create_test(min)
+create_test(over)
+create_test(sum)
+
diff --git a/tests/core/serialize/Avg.cpp b/tests/core/serialize/aggregate_function/avg.cpp
similarity index 85%
rename from tests/core/serialize/Avg.cpp
rename to tests/core/serialize/aggregate_function/avg.cpp
index 2d88ef2c..73c57357 100644
--- a/tests/core/serialize/Avg.cpp
+++ b/tests/core/serialize/aggregate_function/avg.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2023, Roland Bock
+ * Copyright (c) 2023, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -24,10 +24,10 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
-int Avg(int, char* [])
+int main(int, char* [])
 {
   const auto bar = test::TabBar{};
 
@@ -36,13 +36,12 @@ int Avg(int, char* [])
   SQLPP_COMPARE(avg(sqlpp::distinct, bar.id), "AVG(DISTINCT tab_bar.id)");
 
   // Expression.
-#warning: Note that the inner parens aren't necessary.
-  SQLPP_COMPARE(avg(bar.id + 7), "AVG((tab_bar.id + 7))");
-  SQLPP_COMPARE(avg(sqlpp::distinct, bar.id + 7), "AVG(DISTINCT (tab_bar.id + 7))");
+  SQLPP_COMPARE(avg(bar.id + 7), "AVG(tab_bar.id + 7)");
+  SQLPP_COMPARE(avg(sqlpp::distinct, bar.id + 7), "AVG(DISTINCT tab_bar.id + 7)");
 
   // With sub select.
-  SQLPP_COMPARE(avg(select(sqlpp::value(7).as(sqlpp::alias::a))), "AVG((SELECT 7 AS a))");
-  SQLPP_COMPARE(avg(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "AVG(DISTINCT (SELECT 7 AS a))");
+  SQLPP_COMPARE(avg(select(sqlpp::value(7).as(sqlpp::alias::a))), "AVG(SELECT 7 AS a)");
+  SQLPP_COMPARE(avg(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "AVG(DISTINCT SELECT 7 AS a)");
 
   return 0;
 }
diff --git a/tests/core/serialize/Count.cpp b/tests/core/serialize/aggregate_function/count.cpp
similarity index 85%
rename from tests/core/serialize/Count.cpp
rename to tests/core/serialize/aggregate_function/count.cpp
index 6cca2e6d..3a89210b 100644
--- a/tests/core/serialize/Count.cpp
+++ b/tests/core/serialize/aggregate_function/count.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2023, Roland Bock
+ * Copyright (c) 2023, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -24,10 +24,10 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
-int Count(int, char* [])
+int main(int, char* [])
 {
   const auto bar = test::TabBar{};
 
@@ -36,13 +36,12 @@ int Count(int, char* [])
   SQLPP_COMPARE(count(sqlpp::distinct, bar.id), "COUNT(DISTINCT tab_bar.id)");
 
   // Expression.
-#warning: Note that the inner parens aren't necessary.
-  SQLPP_COMPARE(count(bar.id + 7), "COUNT((tab_bar.id + 7))");
-  SQLPP_COMPARE(count(sqlpp::distinct, bar.id + 7), "COUNT(DISTINCT (tab_bar.id + 7))");
+  SQLPP_COMPARE(count(bar.id + 7), "COUNT(tab_bar.id + 7)");
+  SQLPP_COMPARE(count(sqlpp::distinct, bar.id + 7), "COUNT(DISTINCT tab_bar.id + 7)");
 
   // With sub select.
-  SQLPP_COMPARE(count(select(sqlpp::value(7).as(sqlpp::alias::a))), "COUNT((SELECT 7 AS a))");
-  SQLPP_COMPARE(count(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "COUNT(DISTINCT (SELECT 7 AS a))");
+  SQLPP_COMPARE(count(select(sqlpp::value(7).as(sqlpp::alias::a))), "COUNT(SELECT 7 AS a)");
+  SQLPP_COMPARE(count(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "COUNT(DISTINCT SELECT 7 AS a)");
 
   return 0;
 }
diff --git a/tests/core/serialize/Max.cpp b/tests/core/serialize/aggregate_function/max.cpp
similarity index 86%
rename from tests/core/serialize/Max.cpp
rename to tests/core/serialize/aggregate_function/max.cpp
index ecd7e5c1..33988afd 100644
--- a/tests/core/serialize/Max.cpp
+++ b/tests/core/serialize/aggregate_function/max.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2023, Roland Bock
+ * Copyright (c) 2023, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -24,10 +24,10 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
-int Max(int, char* [])
+int main(int, char* [])
 {
   const auto bar = test::TabBar{};
 
@@ -36,13 +36,12 @@ int Max(int, char* [])
   SQLPP_COMPARE(max(sqlpp::distinct, bar.id), "MAX(DISTINCT tab_bar.id)");
 
   // Expression.
-  // Note that the inner parens aren't necessary.
-  SQLPP_COMPARE(max(bar.id + 7), "MAX((tab_bar.id + 7))");
-  SQLPP_COMPARE(max(sqlpp::distinct, bar.id + 7), "MAX(DISTINCT (tab_bar.id + 7))");
+  SQLPP_COMPARE(max(bar.id + 7), "MAX(tab_bar.id + 7)");
+  SQLPP_COMPARE(max(sqlpp::distinct, bar.id + 7), "MAX(DISTINCT tab_bar.id + 7)");
 
   // With sub select.
-  SQLPP_COMPARE(max(select(sqlpp::value(7).as(sqlpp::alias::a))), "MAX((SELECT 7 AS a))");
-  SQLPP_COMPARE(max(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "MAX(DISTINCT (SELECT 7 AS a))");
+  SQLPP_COMPARE(max(select(sqlpp::value(7).as(sqlpp::alias::a))), "MAX(SELECT 7 AS a)");
+  SQLPP_COMPARE(max(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "MAX(DISTINCT SELECT 7 AS a)");
 
   return 0;
 }
diff --git a/tests/core/serialize/Min.cpp b/tests/core/serialize/aggregate_function/min.cpp
similarity index 88%
rename from tests/core/serialize/Min.cpp
rename to tests/core/serialize/aggregate_function/min.cpp
index 96806e0a..c81198c2 100644
--- a/tests/core/serialize/Min.cpp
+++ b/tests/core/serialize/aggregate_function/min.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2023, Roland Bock
+ * Copyright (c) 2023, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -24,10 +24,10 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
-int Min(int, char* [])
+int main(int, char* [])
 {
   const auto bar = test::TabBar{};
 
@@ -37,12 +37,12 @@ int Min(int, char* [])
 
   // Expression.
   // Note that the inner parens aren't necessary.
-  SQLPP_COMPARE(min(bar.id + 7), "MIN((tab_bar.id + 7))");
-  SQLPP_COMPARE(min(sqlpp::distinct, bar.id + 7), "MIN(DISTINCT (tab_bar.id + 7))");
+  SQLPP_COMPARE(min(bar.id + 7), "MIN(tab_bar.id + 7)");
+  SQLPP_COMPARE(min(sqlpp::distinct, bar.id + 7), "MIN(DISTINCT tab_bar.id + 7)");
 
   // With sub select.
-  SQLPP_COMPARE(min(select(sqlpp::value(7).as(sqlpp::alias::a))), "MIN((SELECT 7 AS a))");
-  SQLPP_COMPARE(min(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "MIN(DISTINCT (SELECT 7 AS a))");
+  SQLPP_COMPARE(min(select(sqlpp::value(7).as(sqlpp::alias::a))), "MIN(SELECT 7 AS a)");
+  SQLPP_COMPARE(min(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "MIN(DISTINCT SELECT 7 AS a)");
 
   return 0;
 }
diff --git a/tests/core/serialize/Over.cpp b/tests/core/serialize/aggregate_function/over.cpp
similarity index 71%
rename from tests/core/serialize/Over.cpp
rename to tests/core/serialize/aggregate_function/over.cpp
index 02dcc16a..aa70df8b 100644
--- a/tests/core/serialize/Over.cpp
+++ b/tests/core/serialize/aggregate_function/over.cpp
@@ -24,19 +24,19 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
 SQLPP_ALIAS_PROVIDER(cheese);
 
-int Over(int, char* []) {
+int main(int, char* []) {
   auto const foo = test::TabFoo{};
 
-  SQLPP_COMPARE(select(avg(foo.doubleN).over().as(cheese)), "SELECT AVG(tab_foo.double_n) OVER() AS cheese");
-  SQLPP_COMPARE(select(count(foo.doubleN).over().as(cheese)), "SELECT COUNT(tab_foo.double_n) OVER() AS cheese");
-  SQLPP_COMPARE(select(max(foo.doubleN).over().as(cheese)), "SELECT MAX(tab_foo.double_n) OVER() AS cheese");
-  SQLPP_COMPARE(select(min(foo.doubleN).over().as(cheese)), "SELECT MIN(tab_foo.double_n) OVER() AS cheese");
-  SQLPP_COMPARE(select(sum(foo.doubleN).over().as(cheese)), "SELECT SUM(tab_foo.double_n) OVER() AS cheese");
+  SQLPP_COMPARE(avg(foo.doubleN).over().as(cheese), "AVG(tab_foo.double_n) OVER() AS cheese");
+  SQLPP_COMPARE(count(foo.doubleN).over().as(cheese), "COUNT(tab_foo.double_n) OVER() AS cheese");
+  SQLPP_COMPARE(max(foo.doubleN).over().as(cheese), "MAX(tab_foo.double_n) OVER() AS cheese");
+  SQLPP_COMPARE(min(foo.doubleN).over().as(cheese), "MIN(tab_foo.double_n) OVER() AS cheese");
+  SQLPP_COMPARE(sum(foo.doubleN).over().as(cheese), "SUM(tab_foo.double_n) OVER() AS cheese");
 
   return 0;
 }
diff --git a/tests/core/serialize/Sum.cpp b/tests/core/serialize/aggregate_function/sum.cpp
similarity index 88%
rename from tests/core/serialize/Sum.cpp
rename to tests/core/serialize/aggregate_function/sum.cpp
index e0adeda0..2a7c56f9 100644
--- a/tests/core/serialize/Sum.cpp
+++ b/tests/core/serialize/aggregate_function/sum.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2023, Roland Bock
+ * Copyright (c) 2023, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -24,10 +24,10 @@
  */
 
 #include "Sample.h"
-#include "compare.h"
+#include "../compare.h"
 #include <sqlpp11/sqlpp11.h>
 
-int Sum(int, char* [])
+int main(int, char* [])
 {
   const auto bar = test::TabBar{};
 
@@ -37,12 +37,12 @@ int Sum(int, char* [])
 
   // Expression.
   // Note that the inner parens aren't necessary.
-  SQLPP_COMPARE(sum(bar.id + 7), "SUM((tab_bar.id + 7))");
-  SQLPP_COMPARE(sum(sqlpp::distinct, bar.id + 7), "SUM(DISTINCT (tab_bar.id + 7))");
+  SQLPP_COMPARE(sum(bar.id + 7), "SUM(tab_bar.id + 7)");
+  SQLPP_COMPARE(sum(sqlpp::distinct, bar.id + 7), "SUM(DISTINCT tab_bar.id + 7)");
 
   // With sub select.
-  SQLPP_COMPARE(sum(select(sqlpp::value(7).as(sqlpp::alias::a))), "SUM((SELECT 7 AS a))");
-  SQLPP_COMPARE(sum(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "SUM(DISTINCT (SELECT 7 AS a))");
+  SQLPP_COMPARE(sum(select(sqlpp::value(7).as(sqlpp::alias::a))), "SUM(SELECT 7 AS a)");
+  SQLPP_COMPARE(sum(sqlpp::distinct, select(sqlpp::value(7).as(sqlpp::alias::a))), "SUM(DISTINCT SELECT 7 AS a)");
 
   return 0;
 }