diff --git a/flutter/lib/models/model.dart b/flutter/lib/models/model.dart
index 802a18a52..8f46fdca8 100644
--- a/flutter/lib/models/model.dart
+++ b/flutter/lib/models/model.dart
@@ -371,7 +371,11 @@ class FfiModel with ChangeNotifier {
 
   _updateSessionWidthHeight(String id) {
     parent.target?.canvasModel.updateViewStyle();
-    bind.sessionSetSize(id: id, width: display.width, height: display.height);
+    if (display.width <= 0 || display.height <= 0) {
+      debugPrintStack(label: 'invalid display size (${display.width},${display.height})');
+    } else {
+      bind.sessionSetSize(id: id, width: display.width, height: display.height);
+    }
   }
 
   /// Handle the peer info event based on [evt].
diff --git a/src/ui_cm_interface.rs b/src/ui_cm_interface.rs
index f5c575d43..bd6eab3bf 100644
--- a/src/ui_cm_interface.rs
+++ b/src/ui_cm_interface.rs
@@ -848,7 +848,7 @@ pub fn elevate_portable(_id: i32) {
 #[cfg(any(target_os = "android", target_os = "ios", feature = "flutter"))]
 #[inline]
 pub fn handle_incoming_voice_call(id: i32, accept: bool) {
-    if let Some(client) = CLIENTS.write().unwrap().get_mut(&id) {
+    if let Some(client) = CLIENTS.read().unwrap().get(&id) {
         allow_err!(client.tx.send(Data::VoiceCallResponse(accept)));
     };
 }
@@ -856,7 +856,7 @@ pub fn handle_incoming_voice_call(id: i32, accept: bool) {
 #[cfg(any(target_os = "android", target_os = "ios", feature = "flutter"))]
 #[inline]
 pub fn close_voice_call(id: i32) {
-    if let Some(client) = CLIENTS.write().unwrap().get_mut(&id) {
+    if let Some(client) = CLIENTS.read().unwrap().get(&id) {
         allow_err!(client.tx.send(Data::CloseVoiceCall("".to_owned())));
     };
 }