diff --git a/CRM/Contact/Import/Parser/Contact.php b/CRM/Contact/Import/Parser/Contact.php
index 1980d227d4df..c4261df3cc69 100644
--- a/CRM/Contact/Import/Parser/Contact.php
+++ b/CRM/Contact/Import/Parser/Contact.php
@@ -845,46 +845,8 @@ private function formatProfileContactParams(
         }
       }
       else {
-        if (($customFieldId = CRM_Core_BAO_CustomField::getKeyID($key))) {
-          // for autocomplete transfer hidden value instead of label
-          if ($params[$key] && isset($params[$key . '_id'])) {
-            $value = $params[$key . '_id'];
-          }
-
-          // we need to append time with date
-          if ($params[$key] && isset($params[$key . '_time'])) {
-            $value .= ' ' . $params[$key . '_time'];
-          }
-
-          // if auth source is not checksum / login && $value is blank, do not proceed - CRM-10128
-          if (($session->get('authSrc') & (CRM_Core_Permission::AUTH_SRC_CHECKSUM + CRM_Core_Permission::AUTH_SRC_LOGIN)) == 0 &&
-            ($value == '' || !isset($value))
-          ) {
-            continue;
-          }
-
-          $valueId = NULL;
-
-          //CRM-13596 - check for contact_sub_type_hidden first
-          if (array_key_exists('contact_sub_type_hidden', $params)) {
-            $type = $params['contact_sub_type_hidden'];
-          }
-          else {
-            $type = $data['contact_type'];
-            if (!empty($data['contact_sub_type'])) {
-              $type = CRM_Utils_Array::explodePadded($data['contact_sub_type']);
-            }
-          }
-
-          CRM_Core_BAO_CustomField::formatCustomField($customFieldId,
-            $data['custom'],
-            $value,
-            $type,
-            $valueId,
-            $contactID,
-            FALSE,
-            FALSE
-          );
+        if ((CRM_Core_BAO_CustomField::getKeyID($key))) {
+          $data[$key] = $value;
         }
         elseif ($key === 'edit') {
           continue;
diff --git a/tests/phpunit/CRM/Contact/Import/Form/data/individual_with_custom_checkbox_field.csv b/tests/phpunit/CRM/Contact/Import/Form/data/individual_with_custom_checkbox_field.csv
new file mode 100644
index 000000000000..62d17c04fd92
--- /dev/null
+++ b/tests/phpunit/CRM/Contact/Import/Form/data/individual_with_custom_checkbox_field.csv
@@ -0,0 +1,3 @@
+First Name,Last name,Colour
+Bob,Smith,"Red,Yellow,Blue"
+Mary,Smith,"1,2,3"
diff --git a/tests/phpunit/CRM/Contact/Import/Parser/ContactTest.php b/tests/phpunit/CRM/Contact/Import/Parser/ContactTest.php
index b78b6c7456a1..754ea0c835ce 100644
--- a/tests/phpunit/CRM/Contact/Import/Parser/ContactTest.php
+++ b/tests/phpunit/CRM/Contact/Import/Parser/ContactTest.php
@@ -854,6 +854,52 @@ public function testCustomDataName(): void {
     $this->assertEquals('Y', $contact[$this->getCustomFieldName('select')]);
   }
 
+  /**
+   * Test values import correctly when they are numbers.
+   *
+   * https://lab.civicrm.org/dev/core/-/issues/3850
+   * @throws \CRM_Core_Exception
+   */
+  public function testCustomCheckboxNumericValues(): void {
+    $this->createCustomGroupWithFieldOfType([], 'checkbox', '', [
+      'option_values' => [
+        [
+          'label' => 'Red',
+          'value' => '1',
+          'weight' => 1,
+          'is_active' => 1,
+        ],
+        [
+          'label' => 'Yellow',
+          'value' => '2',
+          'weight' => 2,
+          'is_active' => 1,
+        ],
+        [
+          'label' => 'Blue',
+          'value' => '3',
+          'weight' => 3,
+          'is_active' => 1,
+        ],
+      ],
+    ]);
+    $this->importCSV('individual_with_custom_checkbox_field.csv', [
+      [0 => 'first_name'],
+      [0 => 'last_name'],
+      [0 => $this->getCustomFieldName('checkbox')],
+    ]);
+    $contacts = Contact::get()->addWhere('last_name', '=', 'Smith')
+      ->addSelect($this->getCustomFieldName('checkbox', 4))
+      ->execute();
+    $this->assertCount(2, $contacts);
+    foreach ($contacts as $contact) {
+      $this->assertEquals([1,2,3], $contact[$this->getCustomFieldName('checkbox', 4)]);
+    }
+  }
+
+  public function testCustomAutoComplete() {
+    $this->createCustomGroupWithFieldOfType([], 'autocomplete');
+  }
   /**
    * Test importing in the Preferred Language Field
    *
@@ -2095,6 +2141,8 @@ protected function validateCSV(string $csv, array $mapper, array $submittedValue
    *   e.g [['first_name']['email', 1]].
    *   {@see \CRM_Contact_Import_Parser_Contact::getMappingFieldFromMapperInput}
    * @param array $submittedValues
+   *
+   * @throws \CRM_Core_Exception
    */
   protected function importCSV(string $csv, array $mapper, array $submittedValues = []): void {
     $submittedValues = array_merge([