diff --git a/internal/sync/sync.go b/internal/sync/sync.go
index 7e580d1d..aeb0e30f 100644
--- a/internal/sync/sync.go
+++ b/internal/sync/sync.go
@@ -125,20 +125,17 @@ type loggedWaitGroup struct {
 	sync.WaitGroup
 }
 
-func (wg *loggedWaitGroup) Done() {
+func (wg *loggedWaitGroup) Wait() {
 	start := time.Now()
-	wg.WaitGroup.Done()
+	wg.WaitGroup.Wait()
 	duration := time.Now().Sub(start)
-	if duration > threshold {
+	if duration >= threshold {
 		l.Debugf("WaitGroup took %v at %s", duration, getCaller())
 	}
 }
 
 func getCaller() string {
-	pc := make([]uintptr, 10)
-	runtime.Callers(3, pc)
-	f := runtime.FuncForPC(pc[0])
-	file, line := f.FileLine(pc[0])
+	_, file, line, _ := runtime.Caller(2)
 	file = filepath.Join(filepath.Base(filepath.Dir(file)), filepath.Base(file))
 	return fmt.Sprintf("%s:%d", file, line)
 }
diff --git a/internal/sync/sync_test.go b/internal/sync/sync_test.go
new file mode 100644
index 00000000..6729da03
--- /dev/null
+++ b/internal/sync/sync_test.go
@@ -0,0 +1,177 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package sync
+
+import (
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/calmh/logger"
+)
+
+func TestTypes(t *testing.T) {
+	if _, ok := NewMutex().(*sync.Mutex); !ok {
+		t.Error("Wrong type")
+	}
+
+	if _, ok := NewRWMutex().(*sync.RWMutex); !ok {
+		t.Error("Wrong type")
+	}
+
+	if _, ok := NewWaitGroup().(*sync.WaitGroup); !ok {
+		t.Error("Wrong type")
+	}
+
+	debug = true
+
+	if _, ok := NewMutex().(*loggedMutex); !ok {
+		t.Error("Wrong type")
+	}
+
+	if _, ok := NewRWMutex().(*loggedRWMutex); !ok {
+		t.Error("Wrong type")
+	}
+
+	if _, ok := NewWaitGroup().(*loggedWaitGroup); !ok {
+		t.Error("Wrong type")
+	}
+
+	debug = false
+}
+
+func TestMutex(t *testing.T) {
+	debug = true
+	threshold = time.Millisecond * 5
+
+	msgmut := sync.Mutex{}
+	messages := make([]string, 0)
+
+	l.AddHandler(logger.LevelDebug, func(_ logger.LogLevel, message string) {
+		msgmut.Lock()
+		messages = append(messages, message)
+		msgmut.Unlock()
+	})
+
+	mut := NewMutex()
+	mut.Lock()
+	time.Sleep(2 * time.Millisecond)
+	mut.Unlock()
+
+	if len(messages) > 0 {
+		t.Errorf("Unexpected message count")
+	}
+
+	mut.Lock()
+	time.Sleep(6 * time.Millisecond)
+	mut.Unlock()
+
+	if len(messages) != 1 {
+		t.Errorf("Unexpected message count")
+	}
+
+	debug = false
+}
+
+func TestRWMutex(t *testing.T) {
+	debug = true
+	threshold = time.Millisecond * 5
+
+	msgmut := sync.Mutex{}
+	messages := make([]string, 0)
+
+	l.AddHandler(logger.LevelDebug, func(_ logger.LogLevel, message string) {
+		msgmut.Lock()
+		messages = append(messages, message)
+		msgmut.Unlock()
+	})
+
+	mut := NewRWMutex()
+	mut.Lock()
+	time.Sleep(2 * time.Millisecond)
+	mut.Unlock()
+
+	if len(messages) > 0 {
+		t.Errorf("Unexpected message count")
+	}
+
+	mut.Lock()
+	time.Sleep(6 * time.Millisecond)
+	mut.Unlock()
+
+	if len(messages) != 1 {
+		t.Errorf("Unexpected message count")
+	}
+
+	// Testing rlocker logging
+	mut.RLock()
+	go func() {
+		time.Sleep(7 * time.Millisecond)
+		mut.RUnlock()
+	}()
+
+	mut.Lock()
+	mut.Unlock()
+
+	if len(messages) != 2 {
+		t.Errorf("Unexpected message count")
+	}
+	if !strings.Contains(messages[1], "RUnlockers while locking: sync") || !strings.Contains(messages[1], "sync_test.go:") {
+		t.Error("Unexpected message")
+	}
+
+	// Testing multiple rlockers
+	mut.RLock()
+	mut.RLock()
+	mut.RLock()
+	mut.RUnlock()
+	mut.RUnlock()
+	mut.RUnlock()
+
+	debug = false
+}
+
+func TestWaitGroup(t *testing.T) {
+	debug = true
+	threshold = time.Millisecond * 5
+
+	msgmut := sync.Mutex{}
+	messages := make([]string, 0)
+
+	l.AddHandler(logger.LevelDebug, func(_ logger.LogLevel, message string) {
+		msgmut.Lock()
+		messages = append(messages, message)
+		msgmut.Unlock()
+	})
+
+	wg := NewWaitGroup()
+	wg.Add(1)
+	go func() {
+		time.Sleep(2 * time.Millisecond)
+		wg.Done()
+	}()
+	wg.Wait()
+
+	if len(messages) > 0 {
+		t.Errorf("Unexpected message count")
+	}
+
+	wg = NewWaitGroup()
+	wg.Add(1)
+	go func() {
+		time.Sleep(6 * time.Millisecond)
+		wg.Done()
+	}()
+	wg.Wait()
+
+	if len(messages) != 1 {
+		t.Errorf("Unexpected message count")
+	}
+
+	debug = false
+}