diff --git a/composer.json b/composer.json
index b941542..2487051 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
         "symfony/polyfill-apcu": "^1.6"
     },
     "require-dev": {
-        "phpunit/phpunit": "4.1.0"
+        "phpunit/phpunit": "~5.7"
     },
     "suggest": {
         "ext-redis": "Required if using Redis.",
diff --git a/src/Prometheus/PushGateway.php b/src/Prometheus/PushGateway.php
index a4a3fd2..c788ad8 100644
--- a/src/Prometheus/PushGateway.php
+++ b/src/Prometheus/PushGateway.php
@@ -55,12 +55,12 @@ public function delete($job, $groupingKey = null)
     }
 
     /**
-     * @param CollectorRegistry $collectorRegistry
+     * @param CollectorRegistry|null $collectorRegistry
      * @param $job
      * @param $groupingKey
      * @param $method
      */
-    private function doRequest(CollectorRegistry $collectorRegistry, $job, $groupingKey, $method)
+    private function doRequest(CollectorRegistry $collectorRegistry = null, $job, $groupingKey, $method)
     {
         $url = "http://" . $this->address . "/metrics/job/" . $job;
         if (!empty($groupingKey)) {
diff --git a/src/Prometheus/Storage/Redis.php b/src/Prometheus/Storage/Redis.php
index f38391b..3008118 100644
--- a/src/Prometheus/Storage/Redis.php
+++ b/src/Prometheus/Storage/Redis.php
@@ -62,7 +62,23 @@ public static function setPrefix($prefix)
     public function flushRedis()
     {
         $this->openConnection();
-        $this->redis->flushAll();
+        $this->redis->eval(<<<LUA
+for keyIndex,key in ipairs(KEYS) do
+    local members = redis.call('smembers', key)
+    for memberIndex,member in ipairs(members) do
+       redis.call('del', member)
+    end
+    redis.call('del', key)
+end
+LUA
+            ,
+            array(
+                self::$prefix . Counter::TYPE . self::PROMETHEUS_METRIC_KEYS_SUFFIX,
+                self::$prefix . Gauge::TYPE . self::PROMETHEUS_METRIC_KEYS_SUFFIX,
+                self::$prefix . Histogram::TYPE . self::PROMETHEUS_METRIC_KEYS_SUFFIX,
+            ),
+            3
+        );
     }
 
     /**
diff --git a/tests/Test/Prometheus/Redis/CollectorRegistryTest.php b/tests/Test/Prometheus/Redis/CollectorRegistryTest.php
index 2e69ce9..e09319b 100644
--- a/tests/Test/Prometheus/Redis/CollectorRegistryTest.php
+++ b/tests/Test/Prometheus/Redis/CollectorRegistryTest.php
@@ -4,6 +4,11 @@
 namespace Test\Prometheus\Redis;
 
 use function class_exists;
+use Prometheus\CollectorRegistry;
+use Prometheus\Counter;
+use Prometheus\Gauge;
+use Prometheus\Histogram;
+use Prometheus\RenderTextFormat;
 use Prometheus\Storage\Redis;
 use Test\Prometheus\AbstractCollectorRegistryTest;
 
@@ -17,4 +22,46 @@ public function configureAdapter()
         $this->adapter = new Redis(array('host' => REDIS_HOST));
         $this->adapter->flushRedis();
     }
+
+    /**
+     * @test
+     */
+    public function itShouldOnlyFlushMetricData()
+    {
+        $redis = new \Redis();
+        $redis->connect(REDIS_HOST);
+        $redis->set('foo', 'bar');
+
+        $registry = new CollectorRegistry($this->adapter);
+
+        $counter = $registry->registerCounter('test', 'some_counter', 'it increases', ['type']);
+        $counter->incBy(6, ['blue']);
+        $counterRedisKey = 'PROMETHEUS_' . Counter::TYPE . Redis::PROMETHEUS_METRIC_KEYS_SUFFIX;
+        $this->assertEquals(['PROMETHEUS_:counter:test_some_counter'], $redis->sMembers($counterRedisKey));
+
+        $gauge = $registry->registerGauge('test', 'some_gauge', 'this is for testing', array('foo'));
+        $gauge->set(35, array('bar'));
+        $gaugeRedisKey = 'PROMETHEUS_' . Gauge::TYPE . Redis::PROMETHEUS_METRIC_KEYS_SUFFIX;
+        $this->assertEquals(['PROMETHEUS_:gauge:test_some_gauge'], $redis->sMembers($gaugeRedisKey));
+
+        $histogram = $registry->registerHistogram('test', 'some_histogram', 'this is for testing', array('foo', 'bar'), array(0.1, 1, 5, 10));
+        $histogram->observe(2, array('cat', 'meow'));
+        $histogramRedisKey = 'PROMETHEUS_' . Histogram::TYPE . Redis::PROMETHEUS_METRIC_KEYS_SUFFIX;
+        $this->assertEquals(['PROMETHEUS_:histogram:test_some_histogram'], $redis->sMembers($histogramRedisKey));
+
+        $this->adapter->flushRedis();
+
+        $this->assertEquals('bar', $redis->get('foo'));
+
+        $this->assertEquals([], $redis->sMembers($counterRedisKey));
+        $this->assertFalse($redis->get('PROMETHEUS_:counter:test_some_counter'));
+        $this->assertEquals([], $redis->sMembers($gaugeRedisKey));
+        $this->assertFalse($redis->get('PROMETHEUS_:gauge:test_some_gauge'));
+        $this->assertEquals([], $redis->sMembers($histogramRedisKey));
+        $this->assertFalse($redis->get('PROMETHEUS_:histogram:test_some_histogram'));
+
+        $this->assertEquals("\n", (new RenderTextFormat())->render($registry->getMetricFamilySamples()));
+
+        $redis->del('foo');
+    }
 }