diff --git a/src/Method/CancelReservation.php b/src/Method/CancelReservation.php
index 3344926..18a43dd 100644
--- a/src/Method/CancelReservation.php
+++ b/src/Method/CancelReservation.php
@@ -38,12 +38,13 @@ protected function constructRequestData($data)
 	}
 
 	/**
-	 * @param mixed $data
+	 * @param array $requestData
+	 * @param mixed $responseData
 	 * @return array
 	 */
-	protected function constructResponseData($data)
+	protected function constructResponseData(array $requestData, $responseData)
 	{
-		Validator::checkNull($data);
+		Validator::checkNull($responseData);
 
 		return array();
 	}
diff --git a/src/Method/CheckHealth.php b/src/Method/CheckHealth.php
index cf0f892..9b79c11 100644
--- a/src/Method/CheckHealth.php
+++ b/src/Method/CheckHealth.php
@@ -30,10 +30,11 @@ protected function constructRequestData($data)
 	}
 
 	/**
-	 * @param mixed $data
+	 * @param array $requestData
+	 * @param mixed $responseData
 	 * @return array
 	 */
-	protected function constructResponseData($data)
+	protected function constructResponseData(array $requestData, $responseData)
 	{
 		return array();
 	}
diff --git a/src/Method/CreateReservation.php b/src/Method/CreateReservation.php
index 8d7bf4a..665eb4e 100644
--- a/src/Method/CreateReservation.php
+++ b/src/Method/CreateReservation.php
@@ -38,12 +38,13 @@ protected function constructRequestData($data)
 	}
 
 	/**
-	 * @param mixed $data
+	 * @param array $requestData
+	 * @param mixed $responseData
 	 * @return array
 	 */
-	protected function constructResponseData($data)
+	protected function constructResponseData(array $requestData, $responseData)
 	{
-		Validator::checkNull($data);
+		Validator::checkNull($responseData);
 
 		return array();
 	}
diff --git a/src/Method/GetSlots.php b/src/Method/GetSlots.php
index e8dd3f1..b7a36cf 100644
--- a/src/Method/GetSlots.php
+++ b/src/Method/GetSlots.php
@@ -35,12 +35,13 @@ protected function constructRequestData($data)
 	}
 
 	/**
-	 * @param mixed $data
+	 * @param array $requestData
+	 * @param mixed $responseData
 	 * @return array
 	 */
-	protected function constructResponseData($data)
+	protected function constructResponseData(array $requestData, $responseData)
 	{
-		Validator::checkStructure($data, array(
+		Validator::checkStructure($responseData, array(
 			array(
 				'startDateTime' => Validator::TYPE_DATE_TIME,
 				'endDateTime' => Validator::TYPE_DATE_TIME,
@@ -49,19 +50,25 @@ protected function constructResponseData($data)
 		));
 
 		$result = array();
+		$requestedDate = $requestData[0]->format('Y-m-d');
 
-		foreach ($data as $index => $slot) {
+		foreach ($responseData as $index => $slot) {
 			$whichSlot = sprintf('(slot #%d)', $index + 1);
 			$startDateTime = $slot['startDateTime']->format(DateTime::W3C);
 			$endDateTime = $slot['endDateTime']->format(DateTime::W3C);
+			$startDate = $slot['startDateTime']->format('Y-m-d');
 			$capacity = $slot['capacity'];
 
 			if ($startDateTime >= $endDateTime) {
 				throw new ValidationException(sprintf('Slot startDateTime (%s) must be before endDateTime (%s) %s', $startDateTime, $endDateTime, $whichSlot));
 			}
 
+			if ($requestedDate !== $startDate) {
+				throw new ValidationException(sprintf('Slot startDateTime (%s) does not match requested day (%s) %s', $startDate, $requestedDate, $whichSlot));
+			}
+
 			if ($capacity < 0) {
-				throw new ValidationException(sprintf('Slot capacity (%s) must be non-negative %s', $capacity, $whichSlot));
+				throw new ValidationException(sprintf('Slot capacity (%d) must be non-negative %s', $capacity, $whichSlot));
 			}
 
 			$result[] = array(
diff --git a/src/Method/Method.php b/src/Method/Method.php
index 02830a7..8c22c5e 100644
--- a/src/Method/Method.php
+++ b/src/Method/Method.php
@@ -35,7 +35,7 @@ public function call(Request $request)
 		}
 
 		try {
-			return $this->constructResponseData(call_user_func_array(
+			return $this->constructResponseData($requestData, call_user_func_array(
 				$this->callback,
 				$requestData
 			));
@@ -56,9 +56,10 @@ abstract public function getName();
 	abstract protected function constructRequestData($data);
 
 	/**
-	 * @param mixed $data
+	 * @param array $requestData Return value of constructRequestData
+	 * @param mixed $responseData
 	 * @return array
 	 */
-	abstract protected function constructResponseData($data);
+	abstract protected function constructResponseData(array $requestData, $responseData);
 
 }
diff --git a/tests/src/Method/GetSlotsTest.php b/tests/src/Method/GetSlotsTest.php
index 5e123cf..c0b146e 100644
--- a/tests/src/Method/GetSlotsTest.php
+++ b/tests/src/Method/GetSlotsTest.php
@@ -41,6 +41,9 @@ public function testSuccess()
 	public function testFailures()
 	{
 		$now = new DateTime();
+		$before = new DateTime('-1 hour');
+		$tomorrow = new DateTime('tomorrow');
+		$nowString = $now->format(DateTime::W3C);
 
 		$this->checkException(
 			array(),
@@ -59,25 +62,25 @@ public function testFailures()
 		);
 		$this->checkException(
 			array(
-				'date' => $now->format(DateTime::W3C),
+				'date' => $nowString,
 				'parameters' => array(),
 			),
 			array(
 				array(
-					'startDateTime' => new DateTime(),
+					'startDateTime' => $now,
 				)
 			),
 			'Missing keys (endDateTime, capacity)'
 		);
 		$this->checkException(
 			array(
-				'date' => $now->format(DateTime::W3C),
+				'date' => $nowString,
 				'parameters' => array(),
 			),
 			array(
 				array(
-					'startDateTime' => new DateTime(),
-					'endDateTime' => new DateTime(),
+					'startDateTime' => $now,
+					'endDateTime' => $now,
 					'capacity' => 'string',
 				)
 			),
@@ -85,18 +88,60 @@ public function testFailures()
 		);
 		$this->checkException(
 			array(
-				'date' => $now->format(DateTime::W3C),
+				'date' => $nowString,
 				'parameters' => array(),
 			),
 			array(
 				array(
 					'startDateTime' => 'not-a-datetime',
-					'endDateTime' => new DateTime(),
+					'endDateTime' => $now,
 					'capacity' => 1,
 				)
 			),
 			'DateTime expected, string (not-a-datetime) given.'
 		);
+		$this->checkException(
+			array(
+				'date' => $nowString,
+				'parameters' => array(),
+			),
+			array(
+				array(
+					'startDateTime' => $before,
+					'endDateTime' => $now,
+					'capacity' => -1,
+				)
+			),
+			'Slot capacity (-1) must be non-negative (slot #1)'
+		);
+		$this->checkException(
+			array(
+				'date' => $nowString,
+				'parameters' => array(),
+			),
+			array(
+				array(
+					'startDateTime' => $now,
+					'endDateTime' => $before,
+					'capacity' => 1,
+				)
+			),
+			sprintf('Slot startDateTime (%s) must be before endDateTime (%s) (slot #1)', $nowString, $before->format(DateTime::W3C))
+		);
+		$this->checkException(
+			array(
+				'date' => $tomorrow->format(DateTime::W3C),
+				'parameters' => array(),
+			),
+			array(
+				array(
+					'startDateTime' => $before,
+					'endDateTime' => $now,
+					'capacity' => 1,
+				)
+			),
+			sprintf('Slot startDateTime (%s) does not match requested day (%s) (slot #1)', $now->format('Y-m-d'), $tomorrow->format('Y-m-d'))
+		);
 	}
 
 	/**
@@ -112,7 +157,7 @@ private function checkException(array $requestData, array $responseData, $error)
 				return $responseData;
 			});
 			$method->call($request);
-			$this->fail('Expected exception to be thrown');
+			$this->fail(sprintf('Expected exception with "%s" to be thrown', $error));
 
 		} catch (MethodException $e) {
 			$this->assertContains($error, $e->getMessage());