diff --git a/core/modules/user/src/Exception/ConditionAlreadySetException.php b/core/modules/user/src/Exception/ConditionAlreadySetException.php
new file mode 100644
index 0000000..2a14ece
--- /dev/null
+++ b/core/modules/user/src/Exception/ConditionAlreadySetException.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Drupal\user\Exception;
+
+/**
+ * Thrown by UserDataQuery when a condition has already been set.
+ *
+ * @see \Drupal\user\UserDataQuery
+ */
+class ConditionAlreadySetException extends \Exception {
+}
diff --git a/core/modules/user/src/UserDataQuery.php b/core/modules/user/src/UserDataQuery.php
index 7b26944..c6e5ea1 100644
--- a/core/modules/user/src/UserDataQuery.php
+++ b/core/modules/user/src/UserDataQuery.php
@@ -3,6 +3,7 @@
 namespace Drupal\user;
 
 use Drupal\Core\Database\Query\SelectInterface;
+use Drupal\user\Exception\ConditionAlreadySetException;
 
 /**
  * Returns data stored for a user account.
@@ -10,35 +11,14 @@
 class UserDataQuery implements UserDataQueryInterface {
 
   /**
-   * The name of the module the data is associated with.
+   * Stores which conditions have been set.
    *
-   * @var string
+   * @var array
    */
-  protected $module;
+  protected $sets;
 
   /**
-   * Sets the user account ID the data is associated with.
-   *
-   * @var int
-   */
-  protected $uid;
-
-  /**
-   * The name of the data key.
-   *
-   * @var string
-   */
-  protected $name;
-
-  /**
-   * The value stored.
-   *
-   * @var mixed
-   */
-  protected $value;
-
-  /**
-   * The database connection to use.
+   * The select query on the users_data table.
    *
    * @var \Drupal\Core\Database\Query\SelectInterface
    */
@@ -58,7 +38,7 @@ public function __construct(SelectInterface $select) {
    * {@inheritdoc}
    */
   public function setModule($module) {
-    $this->module = $module;
+    $this->setter('module', $module);
     return $this;
   }
 
@@ -66,7 +46,7 @@ public function setModule($module) {
    * {@inheritdoc}
    */
   public function setUid($uid) {
-    $this->uid = $uid;
+    $this->setter('uid', $uid);
     return $this;
   }
 
@@ -74,7 +54,7 @@ public function setUid($uid) {
    * {@inheritdoc}
    */
   public function setName($name) {
-    $this->name = $name;
+    $this->setter('name', $name);
     return $this;
   }
 
@@ -82,35 +62,42 @@ public function setName($name) {
    * {@inheritdoc}
    */
   public function setValue($value) {
-    $this->value = $value;
+    $is_scalar_value = is_scalar($value);
+    if (!$is_scalar_value) {
+      $value = serialize($value);
+    }
+    $this->setter('value', $value);
+    if (!$is_scalar_value) {
+      $this->select->condition('serialized', 1);
+    }
     return $this;
   }
 
   /**
+   * Sets a condition on the query for the provided name using the value.
+   *
+   * @param string $name
+   *   The name of the field to check.
+   * @param string|int $value
+   *   The value to test the field against.
+   *
+   * @throws \Drupal\user\Exception\ConditionAlreadySetException
+   *   Exception thrown when the select object already has a condition on the
+   *   field.
+   */
+  protected function setter($name, $value) {
+    if (isset($this->sets[$name]) && $this->sets[$name]) {
+      throw new ConditionAlreadySetException("Can not add another condition on '$name'");
+    }
+    $this->select->condition($name, $value);
+    $this->sets[$name] = TRUE;
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function execute() {
-    // Create a query with the supplied conditions.
-    $select = clone $this->select;
-    if ($this->module) {
-      $select->condition('module', $this->module);
-    }
-    if ($this->uid) {
-      $select->condition('uid', $this->uid);
-    }
-    if ($this->name) {
-      $select->condition('name', $this->name);
-    }
-    if ($this->value) {
-      if (!is_scalar($this->value)) {
-        $select->condition('value', serialize($this->value));
-        $select->condition('serialized', 1);
-      }
-      else {
-        $select->condition('value', $this->value);
-      }
-    }
-    foreach ($select->execute() as $row) {
+    foreach ($this->select->execute() as $row) {
       if ($row->serialized) {
         $row->value = unserialize($row->value);
       }
diff --git a/core/modules/user/src/UserDataQueryInterface.php b/core/modules/user/src/UserDataQueryInterface.php
index ac314ff..7271302 100644
--- a/core/modules/user/src/UserDataQueryInterface.php
+++ b/core/modules/user/src/UserDataQueryInterface.php
@@ -12,43 +12,53 @@
   /**
    * Sets the module value.
    *
-   * @param string|null $module
-   *   The name of the module the data is associated with. Use a NULL value to
-   *   unset an already set module.
+   * @param string $module
+   *   The name of the module the data is associated with.
    *
    * @return $this
+   *
+   * @throws \Drupal\user\Exception\ConditionAlreadySetException
+   *   Exception thrown when the select object already has a module condition.
    */
   public function setModule($module);
 
   /**
    * Sets the user account ID the data is associated with.
    *
-   * @param int|null $uid
-   *   The user account ID the data is associated with. Use a NULL value to
-   *   unset an already set user account ID.
+   * @param int $uid
+   *   The user account ID the data is associated with.
    *
    * @return $this
+   *
+   * @throws \Drupal\user\Exception\ConditionAlreadySetException
+   *   Exception thrown when the select object already has a user account ID
+   *   condition.
    */
   public function setUid($uid);
 
   /**
    * Sets the name of the data key.
    *
-   * @param string|null $name
-   *   The name of the data key. Use a NULL value to unset an already set data
-   *   key.
+   * @param string $name
+   *   The name of the data key.
    *
    * @return $this
+   *
+   * @throws \Drupal\user\Exception\ConditionAlreadySetException
+   *   Exception thrown when the select object already has a name condition.
    */
   public function setName($name);
 
   /**
    * Sets the value stored.
    *
-   * @param mixed|null $value
-   *   The value stored. Use a NULL value to unset an already set value.
+   * @param mixed $value
+   *   The value stored.
    *
    * @return $this
+   *
+   * @throws \Drupal\user\Exception\ConditionAlreadySetException
+   *   Exception thrown when the select object already has a value condition.
    */
   public function setValue($value);
 
diff --git a/core/modules/user/tests/src/Kernel/UserDataQueryTest.php b/core/modules/user/tests/src/Kernel/UserDataQueryTest.php
index 1cefc04..2cb4602 100644
--- a/core/modules/user/tests/src/Kernel/UserDataQueryTest.php
+++ b/core/modules/user/tests/src/Kernel/UserDataQueryTest.php
@@ -3,6 +3,7 @@
 namespace Drupal\Tests\user\Kernel;
 
 use Drupal\KernelTests\KernelTestBase;
+use Drupal\user\Exception\ConditionAlreadySetException;
 
 /**
  * @coversDefaultClass \Drupal\user\UserDataQuery
@@ -104,78 +105,75 @@ public function userDataQueryProvider() {
    * @covers ::setUid
    * @covers ::setName
    * @covers ::setValue
+   *
+   * @dataProvider userDataQueryMultipleMethodCallsProvider
+   */
+  public function testUserDataQueryMultipleMethodCalls($method, $name, $value) {
+    $this->setExpectedException(ConditionAlreadySetException::class, "Can not add another condition on '$name'");
+    /** @var \Drupal\user\UserData $user_data */
+    $user_data = \Drupal::service('user.data');
+    $user_data_query = $user_data->getUserDataQuery();
+    $user_data_query->$method($value);
+    $user_data_query->$method($value);
+  }
+
+  /**
+   * Data provider for testUserDataQueryMultipleMethodCalls.
+   *
+   * @return array
+   */
+  public function userDataQueryMultipleMethodCallsProvider() {
+    return [
+      ['setUid', 'uid', 1],
+      ['setModule', 'module', 'test'],
+      ['setName', 'name', 'test'],
+      ['setValue', 'value', 'test'],
+    ];
+  }
+
+  /**
+   * @covers ::execute
+   */
+  public function testEmpty() {
+    /** @var \Drupal\user\UserData $user_data */
+    $user_data = \Drupal::service('user.data');
+    $user_data_query = $user_data->getUserDataQuery();
+    $user_data_query->setUid(101);
+    $this->assertSame([], iterator_to_array($user_data_query->execute()));
+  }
+
+  /**
+   * @covers ::setValue
    * @covers ::execute
    */
-  public function testUserDataQueryMultipleMethodCalls() {
+  public function testSetValue() {
     $contents = [
       [
         'module' => 'test',
         'uid' => '100',
         'name' => 'foo',
-        'value' => 'bar',
-      ],
-      [
-        'module' => 'another_test',
-        'uid' => '101',
-        'name' => 'foo',
-        'value' => 'bar',
-      ],
-      [
-        'module' => 'test',
-        'uid' => '101',
-        'name' => 'foo2',
-        'value' => 'bar2',
+        'value' => NULL,
       ],
     ];
-
     /** @var \Drupal\user\UserData $user_data */
     $user_data = \Drupal::service('user.data');
     foreach ($contents as $row) {
       $user_data->set($row['module'], $row['uid'], $row['name'], $row['value']);
     }
     $user_data_query = $user_data->getUserDataQuery();
-    $user_data_query->setModule('test');
-    $this->assertEquals([(object) $contents[0], (object) $contents[2]], iterator_to_array($user_data_query->execute()));
-
-    $user_data_query->setModule('another_test');
-    $this->assertEquals([(object) $contents[1]], iterator_to_array($user_data_query->execute()));
 
-    $user_data_query->setValue('bar');
-    $this->assertEquals([(object) $contents[1]], iterator_to_array($user_data_query->execute()));
-
-    // Test unsetting something.
-    $user_data_query->setModule(NULL);
-    $this->assertEquals([(object) $contents[0], (object) $contents[1]], iterator_to_array($user_data_query->execute()));
-
-    $user_data_query->setName('foo2');
-    $this->assertEquals([], iterator_to_array($user_data_query->execute()));
-
-    $user_data_query->setValue('bar2')->setModule('test');
-    $this->assertEquals([(object) $contents[2]], iterator_to_array($user_data_query->execute()));
-
-    $user_data_query->setName('does_not_exist');
-    $this->assertEquals([], iterator_to_array($user_data_query->execute()));
-
-    // Test unsetting everything.
-    $user_data_query->setName(NULL)->setValue(NULL)->setModule(NULL);
-    $this->assertEquals([(object) $contents[0], (object) $contents[1], (object) $contents[2]], iterator_to_array($user_data_query->execute()));
-
-    $user_data_query->setUid(100);
+    // Test getting NULL values.
+    $user_data_query->setValue(NULL);
     $this->assertEquals([(object) $contents[0]], iterator_to_array($user_data_query->execute()));
 
-    $user_data_query->setUid(101);
-    $this->assertEquals([(object) $contents[1], (object) $contents[2]], iterator_to_array($user_data_query->execute()));
-  }
-
-  /**
-   * @covers ::execute
-   */
-  public function testEmpty() {
-    /** @var \Drupal\user\UserData $user_data */
-    $user_data = \Drupal::service('user.data');
-    $user_data_query = $user_data->getUserDataQuery();
-    $user_data_query->setUid(101);
-    $this->assertSame([], iterator_to_array($user_data_query->execute()));
+    // Test that catching \Drupal\user\Exception\ConditionAlreadySetException
+    // and re-running the query does not break is the value is not scalar.
+    try {
+      $user_data_query->setValue(['value']);
+    }
+    catch (ConditionAlreadySetException $e) {
+    }
+    $this->assertEquals([(object) $contents[0]], iterator_to_array($user_data_query->execute()));
   }
 
 }