diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index 98d019333ec..ddac196cce2 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -1093,5 +1093,26 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2024022300.02);
     }
 
+    if ($oldversion < 2024030500.01) {
+
+        // Get all "select" custom field shortnames.
+        $fieldshortnames = $DB->get_fieldset('customfield_field', 'shortname', ['type' => 'select']);
+
+        // Ensure any used in custom reports columns are not using integer type aggregation.
+        foreach ($fieldshortnames as $fieldshortname) {
+            $DB->execute("
+                UPDATE {reportbuilder_column}
+                   SET aggregation = NULL
+                 WHERE " . $DB->sql_like('uniqueidentifier', ':uniqueidentifier', false) . "
+                   AND aggregation IN ('avg', 'max', 'min', 'sum')
+            ", [
+                'uniqueidentifier' => '%' . $DB->sql_like_escape(":customfield_{$fieldshortname}"),
+            ]);
+        }
+
+        // Main savepoint reached.
+        upgrade_main_savepoint(true, 2024030500.01);
+    }
+
     return true;
 }
diff --git a/reportbuilder/classes/local/helpers/custom_fields.php b/reportbuilder/classes/local/helpers/custom_fields.php
index e1a1826c886..5ce3e6a83d8 100644
--- a/reportbuilder/classes/local/helpers/custom_fields.php
+++ b/reportbuilder/classes/local/helpers/custom_fields.php
@@ -212,6 +212,10 @@ class custom_fields {
             return column::TYPE_TIMESTAMP;
         }
 
+        if ($field->get('type') === 'select') {
+            return column::TYPE_TEXT;
+        }
+
         if ($datafield === 'intvalue') {
             return column::TYPE_INTEGER;
         }
diff --git a/reportbuilder/tests/local/helpers/custom_fields_test.php b/reportbuilder/tests/local/helpers/custom_fields_test.php
index 477f3d02474..35abb77cf5f 100644
--- a/reportbuilder/tests/local/helpers/custom_fields_test.php
+++ b/reportbuilder/tests/local/helpers/custom_fields_test.php
@@ -97,16 +97,23 @@ class custom_fields_test extends core_reportbuilder_testcase {
         $this->assertCount(5, $columns);
         $this->assertContainsOnlyInstancesOf(column::class, $columns);
 
-        [$column0, $column1, $column2, $column3, $column4] = $columns;
-        $this->assertEqualsCanonicalizing(['Text', 'Textarea', 'Checkbox', 'Date', 'Select'], [
-            $column0->get_title(), $column1->get_title(), $column2->get_title(), $column3->get_title(), $column4->get_title()
-        ]);
+        // Column titles.
+        $this->assertEquals(
+            ['Text', 'Textarea', 'Checkbox', 'Date', 'Select'],
+            array_map(fn(column $column) => $column->get_title(), $columns)
+        );
 
-        $this->assertEquals(column::TYPE_TEXT, $column0->get_type());
-        $this->assertEquals('course', $column0->get_entity_name());
-        $this->assertStringStartsWith('LEFT JOIN {customfield_data}', $column0->get_joins()[0]);
-        // Column of type TEXT is sortable.
-        $this->assertTrue($column0->get_is_sortable());
+        // Column types.
+        $this->assertEquals(
+            [column::TYPE_TEXT, column::TYPE_LONGTEXT, column::TYPE_BOOLEAN, column::TYPE_TIMESTAMP, column::TYPE_TEXT],
+            array_map(fn(column $column) => $column->get_type(), $columns)
+        );
+
+        // Column sortable.
+        $this->assertEquals(
+            [true, false, true, true, true],
+            array_map(fn(column $column) => $column->get_is_sortable(), $columns)
+        );
     }
 
     /**
@@ -116,12 +123,23 @@ class custom_fields_test extends core_reportbuilder_testcase {
         $this->resetAfterTest();
 
         $customfields = $this->generate_customfields();
-        $columns = $customfields->get_columns();
-        $this->assertCount(1, ($columns[0])->get_joins());
 
-        $customfields->add_join('JOIN {test} t ON t.id = id');
+        // By default, we always join on the customfield data table.
         $columns = $customfields->get_columns();
-        $this->assertCount(2, ($columns[0])->get_joins());
+        $joins = $columns[0]->get_joins();
+
+        $this->assertCount(1, $joins);
+        $this->assertStringStartsWith('LEFT JOIN {customfield_data}', $joins[0]);
+
+        // Add additional join.
+        $customfields->add_join('JOIN {test} t ON t.id = id');
+
+        $columns = $customfields->get_columns();
+        $joins = $columns[0]->get_joins();
+
+        $this->assertCount(2, $joins);
+        $this->assertEquals('JOIN {test} t ON t.id = id', $joins[0]);
+        $this->assertStringStartsWith('LEFT JOIN {customfield_data}', $joins[1]);
     }
 
     /**
@@ -131,12 +149,17 @@ class custom_fields_test extends core_reportbuilder_testcase {
         $this->resetAfterTest();
 
         $customfields = $this->generate_customfields();
-        $columns = $customfields->get_columns();
-        $this->assertCount(1, ($columns[0])->get_joins());
 
+        // Add additional joins.
         $customfields->add_joins(['JOIN {test} t ON t.id = id', 'JOIN {test2} t2 ON t2.id = id']);
+
         $columns = $customfields->get_columns();
-        $this->assertCount(3, ($columns[0])->get_joins());
+        $joins = $columns[0]->get_joins();
+
+        $this->assertCount(3, $joins);
+        $this->assertEquals('JOIN {test} t ON t.id = id', $joins[0]);
+        $this->assertEquals('JOIN {test2} t2 ON t2.id = id', $joins[1]);
+        $this->assertStringStartsWith('LEFT JOIN {customfield_data}', $joins[2]);
     }
 
     /**
@@ -151,10 +174,11 @@ class custom_fields_test extends core_reportbuilder_testcase {
         $this->assertCount(5, $filters);
         $this->assertContainsOnlyInstancesOf(filter::class, $filters);
 
-        [$filter0, $filter1, $filter2, $filter3, $filter4] = $filters;
-        $this->assertEqualsCanonicalizing(['Text', 'Textarea', 'Checkbox', 'Date', 'Select'], [
-            $filter0->get_header(), $filter1->get_header(), $filter2->get_header(), $filter3->get_header(), $filter4->get_header()
-        ]);
+        // Filter titles.
+        $this->assertEquals(
+            ['Text', 'Textarea', 'Checkbox', 'Date', 'Select'],
+            array_map(fn(filter $filter) => $filter->get_header(), $filters)
+        );
     }
 
     /**
diff --git a/version.php b/version.php
index bb54388cb5f..4856adee69e 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2024030500.00;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2024030500.01;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.
 $release  = '4.4dev+ (Build: 20240305)'; // Human-friendly version name