diff --git a/streams_map_incoming_bidi.go b/streams_map_incoming_bidi.go
index e88d6397..f7f80a28 100644
--- a/streams_map_incoming_bidi.go
+++ b/streams_map_incoming_bidi.go
@@ -85,6 +85,9 @@ func (m *incomingBidiStreamsMap) GetOrOpenStream(id protocol.StreamID) (streamI,
 	m.mutex.RUnlock()
 
 	m.mutex.Lock()
+	// no need to check the two error conditions from above again
+	// * maxStream can only increase, so if the id was valid before, it definitely is valid now
+	// * highestStream is only modified by this function
 	var start protocol.StreamID
 	if m.highestStream == 0 {
 		start = m.nextStream
diff --git a/streams_map_incoming_generic.go b/streams_map_incoming_generic.go
index dc79b496..40d7b750 100644
--- a/streams_map_incoming_generic.go
+++ b/streams_map_incoming_generic.go
@@ -83,6 +83,9 @@ func (m *incomingItemsMap) GetOrOpenStream(id protocol.StreamID) (item, error) {
 	m.mutex.RUnlock()
 
 	m.mutex.Lock()
+	// no need to check the two error conditions from above again
+	// * maxStream can only increase, so if the id was valid before, it definitely is valid now
+	// * highestStream is only modified by this function
 	var start protocol.StreamID
 	if m.highestStream == 0 {
 		start = m.nextStream
diff --git a/streams_map_incoming_uni.go b/streams_map_incoming_uni.go
index 536b42dd..f9fe97b7 100644
--- a/streams_map_incoming_uni.go
+++ b/streams_map_incoming_uni.go
@@ -85,6 +85,9 @@ func (m *incomingUniStreamsMap) GetOrOpenStream(id protocol.StreamID) (receiveSt
 	m.mutex.RUnlock()
 
 	m.mutex.Lock()
+	// no need to check the two error conditions from above again
+	// * maxStream can only increase, so if the id was valid before, it definitely is valid now
+	// * highestStream is only modified by this function
 	var start protocol.StreamID
 	if m.highestStream == 0 {
 		start = m.nextStream
diff --git a/streams_map_outgoing_bidi.go b/streams_map_outgoing_bidi.go
index d2c92dec..e7d9150b 100644
--- a/streams_map_outgoing_bidi.go
+++ b/streams_map_outgoing_bidi.go
@@ -85,10 +85,11 @@ func (m *outgoingBidiStreamsMap) openStreamImpl() (streamI, error) {
 }
 
 func (m *outgoingBidiStreamsMap) GetStream(id protocol.StreamID) (streamI, error) {
+	m.mutex.RLock()
 	if id >= m.nextStream {
+		m.mutex.RUnlock()
 		return nil, qerr.Error(qerr.InvalidStreamID, fmt.Sprintf("peer attempted to open stream %d", id))
 	}
-	m.mutex.RLock()
 	s := m.streams[id]
 	m.mutex.RUnlock()
 	return s, nil
diff --git a/streams_map_outgoing_generic.go b/streams_map_outgoing_generic.go
index 5a283602..80236c15 100644
--- a/streams_map_outgoing_generic.go
+++ b/streams_map_outgoing_generic.go
@@ -86,10 +86,11 @@ func (m *outgoingItemsMap) openStreamImpl() (item, error) {
 }
 
 func (m *outgoingItemsMap) GetStream(id protocol.StreamID) (item, error) {
+	m.mutex.RLock()
 	if id >= m.nextStream {
+		m.mutex.RUnlock()
 		return nil, qerr.Error(qerr.InvalidStreamID, fmt.Sprintf("peer attempted to open stream %d", id))
 	}
-	m.mutex.RLock()
 	s := m.streams[id]
 	m.mutex.RUnlock()
 	return s, nil
diff --git a/streams_map_outgoing_uni.go b/streams_map_outgoing_uni.go
index 77511b78..fd2701b7 100644
--- a/streams_map_outgoing_uni.go
+++ b/streams_map_outgoing_uni.go
@@ -85,10 +85,11 @@ func (m *outgoingUniStreamsMap) openStreamImpl() (sendStreamI, error) {
 }
 
 func (m *outgoingUniStreamsMap) GetStream(id protocol.StreamID) (sendStreamI, error) {
+	m.mutex.RLock()
 	if id >= m.nextStream {
+		m.mutex.RUnlock()
 		return nil, qerr.Error(qerr.InvalidStreamID, fmt.Sprintf("peer attempted to open stream %d", id))
 	}
-	m.mutex.RLock()
 	s := m.streams[id]
 	m.mutex.RUnlock()
 	return s, nil