diff --git a/src/Runner/ResultCache/DefaultResultCache.php b/src/Runner/ResultCache/DefaultResultCache.php
index a9e1eabb372..e7704d81013 100644
--- a/src/Runner/ResultCache/DefaultResultCache.php
+++ b/src/Runner/ResultCache/DefaultResultCache.php
@@ -87,6 +87,17 @@ public function time(string $id): float
         return $this->times[$id] ?? 0.0;
     }
 
+    public function mergeWith(self $other): void
+    {
+        foreach ($other->defects as $id => $defect) {
+            $this->defects[$id] = $defect;
+        }
+
+        foreach ($other->times as $id => $time) {
+            $this->times[$id] = $time;
+        }
+    }
+
     public function load(): void
     {
         if (!is_file($this->cacheFilename)) {
diff --git a/tests/unit/Runner/ResultCache/DefaultResultCacheTest.php b/tests/unit/Runner/ResultCache/DefaultResultCacheTest.php
index 61af997f59c..c2c4224b1d6 100644
--- a/tests/unit/Runner/ResultCache/DefaultResultCacheTest.php
+++ b/tests/unit/Runner/ResultCache/DefaultResultCacheTest.php
@@ -68,4 +68,32 @@ public function testCanPersistCacheToFile(): void
 
         unlink($cacheFile);
     }
+
+    public function testCanBeMerged(): void
+    {
+        $cacheSourceOne = new DefaultResultCache;
+        $cacheSourceOne->setStatus('status.a', TestStatus::skipped());
+        $cacheSourceOne->setStatus('status.b', TestStatus::incomplete());
+        $cacheSourceOne->setTime('time.a', 1);
+        $cacheSourceOne->setTime('time.b', 2);
+        $cacheSourceTwo = new DefaultResultCache;
+        $cacheSourceTwo->setStatus('status.c', TestStatus::failure());
+        $cacheSourceTwo->setTime('time.c', 4);
+
+        $sum = new DefaultResultCache;
+        $sum->mergeWith($cacheSourceOne);
+
+        $this->assertSame(TestStatus::skipped()->asString(), $sum->status('status.a')->asString());
+        $this->assertSame(TestStatus::incomplete()->asString(), $sum->status('status.b')->asString());
+        $this->assertNotSame(TestStatus::failure()->asString(), $sum->status('status.c')->asString());
+
+        $this->assertSame(1.0, $sum->time('time.a'));
+        $this->assertSame(2.0, $sum->time('time.b'));
+        $this->assertNotSame(4.0, $sum->time('time.c'));
+
+        $sum->mergeWith($cacheSourceTwo);
+
+        $this->assertSame(TestStatus::failure()->asString(), $sum->status('status.c')->asString());
+        $this->assertSame(4.0, $sum->time('time.c'));
+    }
 }