diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/util/MatrixItem.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/util/MatrixItem.kt
index ce50d90cb0..3bf3f66e40 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/util/MatrixItem.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/util/MatrixItem.kt
@@ -132,7 +132,7 @@ sealed class MatrixItem(
 
                     dn.substring(startIndex, startIndex + length)
                 }
-                .toUpperCase(Locale.ROOT)
+                .uppercase(Locale.ROOT)
     }
 
     companion object {
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/verification/SASDefaultVerificationTransaction.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/verification/SASDefaultVerificationTransaction.kt
index c7885ce449..4bf01a2809 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/verification/SASDefaultVerificationTransaction.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/verification/SASDefaultVerificationTransaction.kt
@@ -345,7 +345,7 @@ internal abstract class SASDefaultVerificationTransaction(
     }
 
     protected fun hashUsingAgreedHashMethod(toHash: String): String? {
-        if ("sha256" == accepted?.hash?.toLowerCase(Locale.ROOT)) {
+        if ("sha256" == accepted?.hash?.lowercase(Locale.ROOT)) {
             val olmUtil = OlmUtility()
             val hashBytes = olmUtil.sha256(toHash)
             olmUtil.releaseUtility()
@@ -355,7 +355,7 @@ internal abstract class SASDefaultVerificationTransaction(
     }
 
     private fun macUsingAgreedMethod(message: String, info: String): String? {
-        return when (accepted?.messageAuthenticationCode?.toLowerCase(Locale.ROOT)) {
+        return when (accepted?.messageAuthenticationCode?.lowercase(Locale.ROOT)) {
             SAS_MAC_SHA256_LONGKDF -> getSAS().calculateMacLongKdf(message, info)
             SAS_MAC_SHA256         -> getSAS().calculateMac(message, info)
             else                   -> null
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/identity/IdentityBulkLookupTask.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/identity/IdentityBulkLookupTask.kt
index 4f6e906766..114695062c 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/identity/IdentityBulkLookupTask.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/identity/IdentityBulkLookupTask.kt
@@ -117,7 +117,7 @@ internal class DefaultIdentityBulkLookupTask @Inject constructor(
         return withOlmUtility { olmUtility ->
             threePids.map { threePid ->
                 base64ToBase64Url(
-                        olmUtility.sha256(threePid.value.toLowerCase(Locale.ROOT)
+                        olmUtility.sha256(threePid.value.lowercase(Locale.ROOT)
                                 + " " + threePid.toMedium() + " " + pepper)
                 )
             }
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/util/Hash.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/util/Hash.kt
index e19b1bcca7..47f20913ec 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/util/Hash.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/util/Hash.kt
@@ -27,7 +27,7 @@ fun String.md5() = try {
     digest.update(toByteArray())
     digest.digest()
             .joinToString("") { String.format("%02X", it) }
-            .toLowerCase(Locale.ROOT)
+            .lowercase(Locale.ROOT)
 } catch (exc: Exception) {
     // Should not happen, but just in case
     hashCode().toString()
diff --git a/vector/src/main/java/im/vector/app/core/intent/VectorMimeType.kt b/vector/src/main/java/im/vector/app/core/intent/VectorMimeType.kt
index 1299f4086b..e68b5e1b07 100644
--- a/vector/src/main/java/im/vector/app/core/intent/VectorMimeType.kt
+++ b/vector/src/main/java/im/vector/app/core/intent/VectorMimeType.kt
@@ -45,7 +45,7 @@ fun getMimeTypeFromUri(context: Context, uri: Uri): String? {
 
         if (null != mimeType) {
             // the mimetype is sometimes in uppercase.
-            mimeType = mimeType.toLowerCase(Locale.ROOT)
+            mimeType = mimeType.lowercase(Locale.ROOT)
         }
     } catch (e: Exception) {
         Timber.e(e, "Failed to open resource input stream")
diff --git a/vector/src/main/java/im/vector/app/core/utils/FileUtils.kt b/vector/src/main/java/im/vector/app/core/utils/FileUtils.kt
index b5ce922487..fc9aa692b1 100644
--- a/vector/src/main/java/im/vector/app/core/utils/FileUtils.kt
+++ b/vector/src/main/java/im/vector/app/core/utils/FileUtils.kt
@@ -112,7 +112,7 @@ fun getFileExtension(fileUri: String): String? {
                 val ext = filename.substring(dotPos + 1)
 
                 if (ext.isNotBlank()) {
-                    return ext.toLowerCase(Locale.ROOT)
+                    return ext.lowercase(Locale.ROOT)
                 }
             }
         }
diff --git a/vector/src/main/java/im/vector/app/features/home/room/detail/RoomDetailViewModel.kt b/vector/src/main/java/im/vector/app/features/home/room/detail/RoomDetailViewModel.kt
index cd7f6a5730..3a9969b43c 100644
--- a/vector/src/main/java/im/vector/app/features/home/room/detail/RoomDetailViewModel.kt
+++ b/vector/src/main/java/im/vector/app/features/home/room/detail/RoomDetailViewModel.kt
@@ -449,7 +449,7 @@ class RoomDetailViewModel @AssistedInject constructor(
                 widgetSessionId = widgetSessionId.substring(0, 7)
             }
             val roomId: String = room.roomId
-            val confId = roomId.substring(1, roomId.indexOf(":") - 1) + widgetSessionId.toLowerCase(VectorLocale.applicationLocale)
+            val confId = roomId.substring(1, roomId.indexOf(":") - 1) + widgetSessionId.lowercase(VectorLocale.applicationLocale)
 
             val preferredJitsiDomain = tryOrNull {
                 rawService.getElementWellknown(session.myUserId)
diff --git a/vector/src/main/java/im/vector/app/features/settings/VectorLocale.kt b/vector/src/main/java/im/vector/app/features/settings/VectorLocale.kt
index cff4ca0cb9..f558ba28c6 100644
--- a/vector/src/main/java/im/vector/app/features/settings/VectorLocale.kt
+++ b/vector/src/main/java/im/vector/app/features/settings/VectorLocale.kt
@@ -181,7 +181,7 @@ object VectorLocale {
             }
         }
                 // sort by human display names
-                .sortedBy { localeToLocalisedString(it).toLowerCase(it) }
+                .sortedBy { localeToLocalisedString(it).lowercase(it) }
 
         supportedLocales.clear()
         supportedLocales.addAll(list)