diff --git a/io/src/main/scala/sbt/internal/io/EventMonitor.scala b/io/src/main/scala/sbt/internal/io/EventMonitor.scala
index 3e74106f..cfe7f7ba 100644
--- a/io/src/main/scala/sbt/internal/io/EventMonitor.scala
+++ b/io/src/main/scala/sbt/internal/io/EventMonitor.scala
@@ -130,8 +130,11 @@ private[sbt] object EventMonitor {
       def getFilesForKey(key: WatchKey): collection.Seq[Path] = key match {
         case null => Nil
         case k =>
-          val allEvents = k.pollEvents.asScala
-            .map(e => k.watchable.asInstanceOf[Path].resolve(e.context.asInstanceOf[Path]))
+          val rawEvents = k.pollEvents
+          k.reset()
+          val allEvents = rawEvents.asScala.flatMap { e =>
+            Option(e.context).map(c => k.watchable.asInstanceOf[Path].resolve(c.asInstanceOf[Path]))
+          }
           logger.debug(s"Received events:\n${allEvents.mkString("\n")}")
           val (exist, notExist) = allEvents.partition(Files.exists(_))
           val (updatedDirectories, updatedFiles) = exist.partition(Files.isDirectory(_))
diff --git a/io/src/main/scala/sbt/io/MacOSXWatchService.scala b/io/src/main/scala/sbt/io/MacOSXWatchService.scala
index 68719708..96eae239 100644
--- a/io/src/main/scala/sbt/io/MacOSXWatchService.scala
+++ b/io/src/main/scala/sbt/io/MacOSXWatchService.scala
@@ -155,7 +155,7 @@ private class MacOSXWatchKey(val watchable: JPath, queueSize: Int, kinds: WatchE
     Collections.unmodifiableList(result)
   }
 
-  override def reset(): Boolean = { events.clear(); true }
+  override def reset(): Boolean = true
 
   override def toString = s"MacOSXWatchKey($watchable)"
 
diff --git a/io/src/test/scala/sbt/internal/io/SourceModificationWatchSpec.scala b/io/src/test/scala/sbt/internal/io/SourceModificationWatchSpec.scala
index 8140ea4b..51caa0ff 100644
--- a/io/src/test/scala/sbt/internal/io/SourceModificationWatchSpec.scala
+++ b/io/src/test/scala/sbt/internal/io/SourceModificationWatchSpec.scala
@@ -348,6 +348,30 @@ abstract class SourceModificationWatchSpec(
     } finally monitor.close()
   }
 
+  it should "reset keys" in IO.withTemporaryDirectory { dir =>
+    val parentDir = dir / "src" / "watchme"
+    val file = parentDir / "Foo.scala"
+
+    writeNewFile(file, "foo")
+    // Longer timeout because there are many file system operations
+    val deadline = 5.seconds.fromNow
+    val monitor = defaultMonitor(getService, parentDir, tc = () => deadline.isOverdue)
+    try {
+      val n = 1000
+      val triggered0 = watchTest(monitor) {
+        (0 to n).foreach(i => IO.write(parentDir / s"Foo$i.scala", s"foo$i"))
+      }
+      assert(triggered0)
+      assert(IO.read(file) == s"foo")
+
+      val triggered1 = watchTest(monitor) {
+        IO.write(file, "baz")
+      }
+      assert(triggered1)
+      assert(IO.read(file) == "baz")
+    } finally monitor.close()
+  }
+
   "WatchService.poll" should "throw a `ClosedWatchServiceException` if used after `close`" in {
     val service = getService
     service.close()