diff --git a/app/src/main/java/net/moasdawiki/app/CalendarSyncAdapter.java b/app/src/main/java/net/moasdawiki/app/CalendarSyncAdapter.java
index 8269e45..eb1262e 100644
--- a/app/src/main/java/net/moasdawiki/app/CalendarSyncAdapter.java
+++ b/app/src/main/java/net/moasdawiki/app/CalendarSyncAdapter.java
@@ -286,8 +286,7 @@ public class CalendarSyncAdapter extends AbstractThreadedSyncAdapter {
                 if (!ActivityCompat.shouldShowRequestPermissionRationale(activity, Manifest.permission.WRITE_CALENDAR)) {
                     Log.d(TAG, "User has permanently denied permission WRITE_CALENDAR, informing him");
                     String hint = context.getString(R.string.calendar_permission_request, "WRITE_CALENDAR");
-                    Toast toast = Toast.makeText(context, hint, Toast.LENGTH_SHORT);
-                    toast.show();
+                    activity.runOnUiThread(() -> Toast.makeText(context, hint, Toast.LENGTH_SHORT).show());
                 }
                 Log.d(TAG, "Ask for permission WRITE_CALENDAR");
                 ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.WRITE_CALENDAR}, 0);
@@ -297,8 +296,7 @@ public class CalendarSyncAdapter extends AbstractThreadedSyncAdapter {
                 if (!ActivityCompat.shouldShowRequestPermissionRationale(activity, Manifest.permission.READ_CALENDAR)) {
                     Log.d(TAG, "User has permanently denied permission READ_CALENDAR, informing him");
                     String hint = context.getString(R.string.calendar_permission_request, "READ_CALENDAR");
-                    Toast toast = Toast.makeText(context, hint, Toast.LENGTH_SHORT);
-                    toast.show();
+                    activity.runOnUiThread(() -> Toast.makeText(context, hint, Toast.LENGTH_SHORT).show());
                 }
                 Log.d(TAG, "Ask for permission READ_CALENDAR");
                 ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.READ_CALENDAR}, 0);
diff --git a/app/src/main/java/net/moasdawiki/app/MainActivity.java b/app/src/main/java/net/moasdawiki/app/MainActivity.java
index 35495ed..f858f03 100644
--- a/app/src/main/java/net/moasdawiki/app/MainActivity.java
+++ b/app/src/main/java/net/moasdawiki/app/MainActivity.java
@@ -358,26 +358,30 @@ public class MainActivity extends AppCompatActivity {
     private void runSynchronizationWithServer() {
         int filesCount;
         try {
-            filesCount = synchronizeWikiClient.synchronizeRepository(this::showProgressBar);
+            filesCount = synchronizeWikiClient.synchronizeRepository(this::syncProgress);
         } catch (ServiceException e) {
             Log.e(TAG, "Error synchronizing repository with server", e);
-            showToast(getString(R.string.settings_synchronize_failed));
+            runOnUiThread(() -> showToast(getString(R.string.settings_synchronize_failed)));
             return;
         }
 
         if (filesCount > 0) {
-            showToast(getString(R.string.settings_synchronize_successful, filesCount));
+            runOnUiThread(() -> showToast(getString(R.string.settings_synchronize_successful, filesCount)));
 
             WikiEngineApplication app = (WikiEngineApplication) getApplication();
             app.resetServices();
 
             CalendarSyncAdapter.requestCalendarSync(this);
         } else {
-            showToast(getString(R.string.settings_synchronize_not_necessary));
+            runOnUiThread(() -> showToast(getString(R.string.settings_synchronize_not_necessary)));
         }
 
-        hideProgressBar();
-        updateLayoutVisibility();
+        runOnUiThread(this::hideProgressBar);
+        runOnUiThread(this::updateLayoutVisibility);
+    }
+
+    private void syncProgress(int progress, int max) {
+        runOnUiThread(() -> showProgressBar(progress, max));
     }
 
     /**