diff --git a/main.cc b/main.cc
index 772a2de..1a487ea 100644
--- a/main.cc
+++ b/main.cc
@@ -214,14 +214,16 @@ class Env final : public nf7::Env {
     f.Handle(e);
 
     // trigger file watcher
-    auto itr = watchers_map_.find(e.id);
-    if (itr != watchers_map_.end()) {
+    auto itr = watchers_.find(e.id);
+    if (itr != watchers_.end()) {
       for (auto w : itr->second) w->Handle(e);
     }
 
     // trigger global watcher
-    for (auto w : watchers_map_[0]) w->Handle(e);
-
+    itr = watchers_.find(0);
+    if (itr != watchers_.end()) {
+      for (auto w : itr->second) w->Handle(e);
+    }
     return &f;
   } catch (nf7::ExpiredException&) {
     return nullptr;
@@ -269,15 +271,17 @@ class Env final : public nf7::Env {
   }
 
   void AddWatcher(nf7::File::Id id, nf7::Env::Watcher& w) noexcept override {
-    watchers_map_[id].push_back(&w);
-    watchers_rmap_[&w].push_back(id);
+    watchers_[id].push_back(&w);
   }
-  void RemoveWatcher(nf7::Env::Watcher& w) noexcept override {
-    for (const auto id : watchers_rmap_[&w]) {
-      auto& v = watchers_map_[id];
+  void RemoveWatcher(nf7::File::Id id, nf7::Env::Watcher& w) noexcept override {
+    auto itr = watchers_.find(id);
+    if (watchers_.end() != itr) {
+      auto& v = itr->second;
       v.erase(std::remove(v.begin(), v.end(), &w), v.end());
+      if (v.size() == 0) {
+        watchers_.erase(itr);
+      }
     }
-    watchers_rmap_.erase(&w);
   }
 
  private:
@@ -288,8 +292,7 @@ class Env final : public nf7::Env {
   nf7::File::Id file_next_ = 1;
   std::unordered_map<nf7::File::Id, nf7::File*> files_;
 
-  std::unordered_map<nf7::File::Id, std::vector<nf7::Env::Watcher*>> watchers_map_;
-  std::unordered_map<nf7::Env::Watcher*, std::vector<nf7::File::Id>> watchers_rmap_;
+  std::unordered_map<nf7::File::Id, std::vector<nf7::Env::Watcher*>> watchers_;
 };
 
 
diff --git a/nf7.cc b/nf7.cc
index f046c62..6251da7 100644
--- a/nf7.cc
+++ b/nf7.cc
@@ -265,10 +265,22 @@ File& Env::GetFileOrThrow(File::Id id) const {
 Env::Watcher::Watcher(Env& env) noexcept : env_(&env) {
 }
 Env::Watcher::~Watcher() noexcept {
-  env_->RemoveWatcher(*this);
+  for (auto id : targets_) {
+    env_->RemoveWatcher(id, *this);
+  }
 }
 void Env::Watcher::Watch(File::Id id) noexcept {
-  env_->AddWatcher(id, *this);
+  if (targets_.end() == std::find(targets_.begin(), targets_.end(), id)) {
+    targets_.push_back(id);
+    env_->AddWatcher(id, *this);
+  }
+}
+void Env::Watcher::Unwatch(File::Id id) noexcept {
+  auto itr = std::remove(targets_.begin(), targets_.end(), id);
+  if (itr != targets_.end()) {
+    targets_.erase(itr);
+    env_->RemoveWatcher(id, *this);
+  }
 }
 
 
diff --git a/nf7.hh b/nf7.hh
index be4f52f..e608117 100644
--- a/nf7.hh
+++ b/nf7.hh
@@ -302,7 +302,7 @@ class Env {
   virtual void RemoveFile(File::Id) noexcept = 0;
 
   virtual void AddWatcher(File::Id, Watcher&) noexcept = 0;
-  virtual void RemoveWatcher(Watcher&) noexcept = 0;
+  virtual void RemoveWatcher(File::Id, Watcher&) noexcept = 0;
 
  private:
   std::filesystem::path npath_;
@@ -316,12 +316,17 @@ class Env::Watcher {
   Watcher& operator=(const Watcher&) = delete;
   Watcher& operator=(Watcher&&) = delete;
 
+  void Watch(File::Id) noexcept;
+  void Unwatch(File::Id) noexcept;
+
   virtual void Handle(const File::Event&) noexcept = 0;
 
-  void Watch(File::Id) noexcept;
+  const std::vector<File::Id>& targets() const noexcept { return targets_; }
 
  private:
   Env* const env_;
+
+  std::vector<File::Id> targets_;
 };