diff --git a/app/build.gradle b/app/build.gradle
index f61d1dd6a..10b55c802 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -115,7 +115,7 @@ android {
 
     android.applicationVariants.all { variant ->
         String variantName = variant.name
-        String capVariantName = variantName.substring(0, 1).toUpperCase() + variantName.substring(1)
+        String capVariantName = variantName.substring(0, 1).toUpperCase(Locale.ROOT) + variantName.substring(1)
         tasks.register("spotbugs${capVariantName}Report", SpotBugsTask) {
             ignoreFailures = true // should continue checking
             effort = "max"
diff --git a/app/src/main/java/com/nextcloud/talk/controllers/ContactsController.java b/app/src/main/java/com/nextcloud/talk/controllers/ContactsController.java
index 3d202cfd4..c9dbaf36a 100644
--- a/app/src/main/java/com/nextcloud/talk/controllers/ContactsController.java
+++ b/app/src/main/java/com/nextcloud/talk/controllers/ContactsController.java
@@ -80,6 +80,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
@@ -540,7 +541,8 @@ public class ContactsController extends BaseController implements SearchView.OnQ
                                         } else if (participant.getActorType() == Participant.ActorType.CIRCLES) {
                                             headerTitle = getResources().getString(R.string.nc_circles);
                                         } else {
-                                            headerTitle = participant.getDisplayName().substring(0, 1).toUpperCase();
+                                            headerTitle =
+                                                participant.getDisplayName().substring(0, 1).toUpperCase(Locale.getDefault());
                                         }
 
                                         GenericTextHeaderItem genericTextHeaderItem;
diff --git a/app/src/main/java/com/nextcloud/talk/webrtc/MagicWebRTCUtils.java b/app/src/main/java/com/nextcloud/talk/webrtc/MagicWebRTCUtils.java
index 9989203e5..68a8a3c74 100644
--- a/app/src/main/java/com/nextcloud/talk/webrtc/MagicWebRTCUtils.java
+++ b/app/src/main/java/com/nextcloud/talk/webrtc/MagicWebRTCUtils.java
@@ -92,8 +92,8 @@ public class MagicWebRTCUtils {
 
 
     public static boolean shouldEnableVideoHardwareAcceleration() {
-        return (!HARDWARE_ACCELERATION_VENDOR_BLACKLIST.contains(Build.MANUFACTURER.toLowerCase())
-                && !HARDWARE_ACCELERATION_DEVICE_BLACKLIST.contains(Build.MODEL.toUpperCase()));
+        return (!HARDWARE_ACCELERATION_VENDOR_BLACKLIST.contains(Build.MANUFACTURER.toLowerCase(Locale.ROOT))
+                && !HARDWARE_ACCELERATION_DEVICE_BLACKLIST.contains(Build.MODEL.toUpperCase(Locale.ROOT)));
     }
 
     public static String preferCodec(String sdpDescription, String codec, boolean isAudio) {