diff --git a/lib/protocol/common_test.go b/lib/protocol/common_test.go
index 8f1028078..6db987d97 100644
--- a/lib/protocol/common_test.go
+++ b/lib/protocol/common_test.go
@@ -8,20 +8,21 @@ import (
 )
 
 type TestModel struct {
-	data     []byte
-	folder   string
-	name     string
-	offset   int64
-	size     int
-	hash     []byte
-	flags    uint32
-	options  []Option
-	closedCh chan bool
+	data      []byte
+	folder    string
+	name      string
+	offset    int64
+	size      int
+	hash      []byte
+	flags     uint32
+	options   []Option
+	closedCh  chan struct{}
+	closedErr error
 }
 
 func newTestModel() *TestModel {
 	return &TestModel{
-		closedCh: make(chan bool),
+		closedCh: make(chan struct{}),
 	}
 }
 
@@ -44,18 +45,19 @@ func (t *TestModel) Request(deviceID DeviceID, folder, name string, offset int64
 }
 
 func (t *TestModel) Close(deviceID DeviceID, err error) {
+	t.closedErr = err
 	close(t.closedCh)
 }
 
 func (t *TestModel) ClusterConfig(deviceID DeviceID, config ClusterConfigMessage) {
 }
 
-func (t *TestModel) isClosed() bool {
+func (t *TestModel) closedError() error {
 	select {
 	case <-t.closedCh:
-		return true
+		return t.closedErr
 	case <-time.After(1 * time.Second):
-		return false // Timeout
+		return nil // Timeout
 	}
 }
 
diff --git a/lib/protocol/protocol.go b/lib/protocol/protocol.go
index 0144b4e6d..edcb75ff5 100644
--- a/lib/protocol/protocol.go
+++ b/lib/protocol/protocol.go
@@ -691,6 +691,7 @@ func (c *rawConnection) writerLoop() {
 
 func (c *rawConnection) close(err error) {
 	c.once.Do(func() {
+		l.Debugln("close due to", err)
 		close(c.closed)
 
 		c.awaitingMut.Lock()
diff --git a/lib/protocol/protocol_test.go b/lib/protocol/protocol_test.go
index 1556b6c19..d9c0db957 100644
--- a/lib/protocol/protocol_test.go
+++ b/lib/protocol/protocol_test.go
@@ -6,6 +6,7 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -107,14 +108,14 @@ func TestVersionErr(t *testing.T) {
 
 	w := xdr.NewWriter(c0.cw)
 	w.WriteUint32(encodeHeader(header{
-		version: 2,
+		version: 2, // higher than supported
 		msgID:   0,
-		msgType: 0,
+		msgType: messageTypeIndex,
 	}))
 	w.WriteUint32(0) // Avoids reader closing due to EOF
 
-	if !m1.isClosed() {
-		t.Error("Connection should close due to unknown version")
+	if err := m1.closedError(); err == nil || !strings.Contains(err.Error(), "unknown protocol version") {
+		t.Error("Connection should close due to unknown version, not", err)
 	}
 }
 
@@ -140,8 +141,8 @@ func TestTypeErr(t *testing.T) {
 	}))
 	w.WriteUint32(0) // Avoids reader closing due to EOF
 
-	if !m1.isClosed() {
-		t.Error("Connection should close due to unknown message type")
+	if err := m1.closedError(); err == nil || !strings.Contains(err.Error(), "unknown message type") {
+		t.Error("Connection should close due to unknown message type, not", err)
 	}
 }
 
@@ -159,10 +160,10 @@ func TestClose(t *testing.T) {
 	c0.ClusterConfig(ClusterConfigMessage{})
 	c1.ClusterConfig(ClusterConfigMessage{})
 
-	c0.close(nil)
+	c0.close(errors.New("manual close"))
 
 	<-c0.closed
-	if !m0.isClosed() {
+	if err := m0.closedError(); err == nil || !strings.Contains(err.Error(), "manual close") {
 		t.Fatal("Connection should be closed")
 	}