diff --git a/internal/lsp/cache/cache.go b/internal/lsp/cache/cache.go
index b5eaa15e..cdb1d490 100644
--- a/internal/lsp/cache/cache.go
+++ b/internal/lsp/cache/cache.go
@@ -28,9 +28,10 @@ type cache struct {
 
 func (c *cache) NewSession(log xlog.Logger) source.Session {
 	return &session{
-		cache:    c,
-		log:      log,
-		overlays: make(map[span.URI]*source.FileContent),
+		cache:         c,
+		log:           log,
+		overlays:      make(map[span.URI]*source.FileContent),
+		filesWatchMap: NewWatchMap(),
 	}
 }
 
diff --git a/internal/lsp/cache/file.go b/internal/lsp/cache/file.go
index 70c588bc..d0683ebe 100644
--- a/internal/lsp/cache/file.go
+++ b/internal/lsp/cache/file.go
@@ -18,7 +18,6 @@ import (
 // viewFile extends source.File with helper methods for the view package.
 type viewFile interface {
 	source.File
-	invalidate()
 	filename() string
 	addURI(uri span.URI) int
 }
diff --git a/internal/lsp/cache/session.go b/internal/lsp/cache/session.go
index 53dee8a5..21091535 100644
--- a/internal/lsp/cache/session.go
+++ b/internal/lsp/cache/session.go
@@ -27,7 +27,8 @@ type session struct {
 	overlayMu sync.Mutex
 	overlays  map[span.URI]*source.FileContent
 
-	openFiles sync.Map
+	openFiles     sync.Map
+	filesWatchMap *WatchMap
 }
 
 func (s *session) Shutdown(ctx context.Context) {
@@ -184,8 +185,10 @@ func (s *session) ReadFile(uri span.URI) *source.FileContent {
 
 func (s *session) SetOverlay(uri span.URI, data []byte) {
 	s.overlayMu.Lock()
-	defer s.overlayMu.Unlock()
-	//TODO: we also need to invoke and watchers in here
+	defer func() {
+		s.overlayMu.Unlock()
+		s.filesWatchMap.Notify(uri)
+	}()
 	if data == nil {
 		delete(s.overlays, uri)
 		return
diff --git a/internal/lsp/cache/view.go b/internal/lsp/cache/view.go
index 32204e84..7908f0b6 100644
--- a/internal/lsp/cache/view.go
+++ b/internal/lsp/cache/view.go
@@ -207,7 +207,7 @@ func (v *view) SetContent(ctx context.Context, uri span.URI, content []byte) err
 	v.backgroundCtx, v.cancel = context.WithCancel(v.baseCtx)
 
 	v.contentChanges[uri] = func() {
-		v.applyContentChange(uri, content)
+		v.session.SetOverlay(uri, content)
 	}
 
 	return nil
@@ -232,17 +232,6 @@ func (v *view) applyContentChanges(ctx context.Context) error {
 	return nil
 }
 
-// applyContentChange applies a content update for a given file. It assumes that the
-// caller is holding the view's mutex.
-func (v *view) applyContentChange(uri span.URI, content []byte) {
-	v.session.SetOverlay(uri, content)
-	f, err := v.getFile(uri)
-	if err != nil {
-		return
-	}
-	f.invalidate()
-}
-
 func (f *goFile) invalidate() {
 	// TODO(rstambler): Should we recompute these here?
 	f.ast = nil
@@ -331,7 +320,9 @@ func (v *view) getFile(uri span.URI) (viewFile, error) {
 	default:
 		return nil, fmt.Errorf("unsupported file extension: %s", ext)
 	}
-
+	v.session.filesWatchMap.Watch(uri, func() {
+		f.invalidate()
+	})
 	v.mapFile(uri, f)
 	return f, nil
 }
diff --git a/internal/lsp/cache/watcher.go b/internal/lsp/cache/watcher.go
new file mode 100644
index 00000000..c8f619b1
--- /dev/null
+++ b/internal/lsp/cache/watcher.go
@@ -0,0 +1,56 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cache
+
+import (
+	"sync"
+)
+
+type watcher struct {
+	id       uint64
+	callback func()
+}
+
+type WatchMap struct {
+	mu       sync.Mutex
+	nextID   uint64
+	watchers map[interface{}][]watcher
+}
+
+func NewWatchMap() *WatchMap {
+	return &WatchMap{watchers: make(map[interface{}][]watcher)}
+}
+func (w *WatchMap) Watch(key interface{}, callback func()) func() {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	id := w.nextID
+	w.nextID++
+	w.watchers[key] = append(w.watchers[key], watcher{
+		id:       id,
+		callback: callback,
+	})
+	return func() {
+		// unwatch if invoked
+		w.mu.Lock()
+		defer w.mu.Unlock()
+		// find and delete the watcher entry
+		entries := w.watchers[key]
+		for i, entry := range entries {
+			if entry.id == id {
+				// found it
+				entries[i] = entries[len(entries)-1]
+				entries = entries[:len(entries)-1]
+			}
+		}
+	}
+}
+
+func (w *WatchMap) Notify(key interface{}) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	for _, entry := range w.watchers[key] {
+		entry.callback()
+	}
+}