diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/MatrixConstants.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/MatrixConstants.kt
new file mode 100644
index 0000000000..49520f3678
--- /dev/null
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/MatrixConstants.kt
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2021 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api
+
+/**
+ * This object define some global constants regarding the Matrix specification
+ */
+object MatrixConstants {
+    /**
+     * Max length for an alias. Room aliases MUST NOT exceed 255 bytes (including the # sigil and the domain).
+     * See [maxAliasLocalPartLength]
+     * Ref. https://matrix.org/docs/spec/appendices#room-aliases
+     */
+    const val ALIAS_MAX_LENGTH = 255
+
+    fun maxAliasLocalPartLength(domain: String): Int {
+        return (ALIAS_MAX_LENGTH - 1 /* # sigil */ - 1 /* ':' */ - domain.length)
+                .coerceAtLeast(0)
+    }
+}
diff --git a/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateRoomController.kt b/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateRoomController.kt
index 70e37b618b..7dd9cb4e00 100644
--- a/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateRoomController.kt
+++ b/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateRoomController.kt
@@ -29,6 +29,7 @@ import im.vector.app.features.form.formEditTextItem
 import im.vector.app.features.form.formEditableAvatarItem
 import im.vector.app.features.form.formSubmitButtonItem
 import im.vector.app.features.form.formSwitchItem
+import org.matrix.android.sdk.api.MatrixConstants
 import org.matrix.android.sdk.api.extensions.orFalse
 import org.matrix.android.sdk.api.session.room.failure.CreateRoomFailure
 import org.matrix.android.sdk.api.session.room.model.RoomJoinRules
@@ -141,7 +142,7 @@ class CreateRoomController @Inject constructor(
                 value(viewState.aliasLocalPart)
                 suffixText(":" + viewState.homeServerName)
                 prefixText("#")
-                maxLength(255)
+                maxLength(MatrixConstants.maxAliasLocalPartLength(viewState.homeServerName))
                 hint(host.stringProvider.getString(R.string.room_alias_address_hint))
                 errorMessage(
                         host.roomAliasErrorFormatter.format(
diff --git a/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateSubSpaceController.kt b/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateSubSpaceController.kt
index 6d292c85da..26ea2f30a3 100644
--- a/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateSubSpaceController.kt
+++ b/vector/src/main/java/im/vector/app/features/roomdirectory/createroom/CreateSubSpaceController.kt
@@ -28,6 +28,7 @@ import im.vector.app.features.form.formEditTextItem
 import im.vector.app.features.form.formEditableSquareAvatarItem
 import im.vector.app.features.form.formMultiLineEditTextItem
 import im.vector.app.features.form.formSubmitButtonItem
+import org.matrix.android.sdk.api.MatrixConstants
 import org.matrix.android.sdk.api.session.room.failure.CreateRoomFailure
 import org.matrix.android.sdk.api.session.room.model.RoomJoinRules
 import javax.inject.Inject
@@ -81,6 +82,7 @@ class CreateSubSpaceController @Inject constructor(
                 hint(host.stringProvider.getString(R.string.create_space_alias_hint))
                 suffixText(":" + data.homeServerName)
                 prefixText("#")
+                maxLength(MatrixConstants.maxAliasLocalPartLength(data.homeServerName))
                 errorMessage(
                         host.roomAliasErrorFormatter.format(
                                 (((data.asyncCreateRoomRequest as? Fail)?.error) as? CreateRoomFailure.AliasError)?.aliasError)
diff --git a/vector/src/main/java/im/vector/app/features/roomprofile/alias/RoomAliasController.kt b/vector/src/main/java/im/vector/app/features/roomprofile/alias/RoomAliasController.kt
index a14bb61606..206f97f184 100644
--- a/vector/src/main/java/im/vector/app/features/roomprofile/alias/RoomAliasController.kt
+++ b/vector/src/main/java/im/vector/app/features/roomprofile/alias/RoomAliasController.kt
@@ -36,6 +36,7 @@ import im.vector.app.features.discovery.settingsInfoItem
 import im.vector.app.features.form.formEditTextItem
 import im.vector.app.features.form.formSwitchItem
 import im.vector.app.features.roomdirectory.createroom.RoomAliasErrorFormatter
+import org.matrix.android.sdk.api.MatrixConstants
 import org.matrix.android.sdk.api.session.room.alias.RoomAliasError
 import org.matrix.android.sdk.api.session.room.model.RoomDirectoryVisibility
 import org.matrix.android.sdk.api.session.room.model.RoomType
@@ -253,6 +254,7 @@ class RoomAliasController @Inject constructor(
                     value(data.newLocalAliasState.value)
                     suffixText(":" + data.homeServerName)
                     prefixText("#")
+                    maxLength(MatrixConstants.maxAliasLocalPartLength(data.homeServerName))
                     hint(host.stringProvider.getString(R.string.room_alias_address_hint))
                     errorMessage(host.roomAliasErrorFormatter.format((data.newLocalAliasState.asyncRequest as? Fail)?.error as? RoomAliasError))
                     onTextChange { value ->
diff --git a/vector/src/main/java/im/vector/app/features/spaces/create/CreateSpaceState.kt b/vector/src/main/java/im/vector/app/features/spaces/create/CreateSpaceState.kt
index 6fb5853269..ab7fb0cc25 100644
--- a/vector/src/main/java/im/vector/app/features/spaces/create/CreateSpaceState.kt
+++ b/vector/src/main/java/im/vector/app/features/spaces/create/CreateSpaceState.kt
@@ -28,7 +28,7 @@ data class CreateSpaceState(
         val step: Step = Step.ChooseType,
         val spaceType: SpaceType? = null,
         val spaceTopology: SpaceTopology? = null,
-        val homeServerName: String? = null,
+        val homeServerName: String = "",
         val aliasLocalPart: String? = null,
         val aliasManuallyModified: Boolean = false,
         val aliasVerificationTask: Async<Boolean> = Uninitialized,
diff --git a/vector/src/main/java/im/vector/app/features/spaces/create/SpaceDetailEpoxyController.kt b/vector/src/main/java/im/vector/app/features/spaces/create/SpaceDetailEpoxyController.kt
index 3789e501c1..14b0db2cd1 100644
--- a/vector/src/main/java/im/vector/app/features/spaces/create/SpaceDetailEpoxyController.kt
+++ b/vector/src/main/java/im/vector/app/features/spaces/create/SpaceDetailEpoxyController.kt
@@ -27,6 +27,7 @@ import im.vector.app.features.form.formEditableSquareAvatarItem
 import im.vector.app.features.form.formMultiLineEditTextItem
 import im.vector.app.features.home.AvatarRenderer
 import im.vector.app.features.roomdirectory.createroom.RoomAliasErrorFormatter
+import org.matrix.android.sdk.api.MatrixConstants
 import org.matrix.android.sdk.api.session.room.alias.RoomAliasError
 import org.matrix.android.sdk.api.util.MatrixItem
 import javax.inject.Inject
@@ -94,8 +95,7 @@ class SpaceDetailEpoxyController @Inject constructor(
                 hint(host.stringProvider.getString(R.string.create_space_alias_hint))
                 suffixText(":" + data.homeServerName)
                 prefixText("#")
-                // spaces alias are limited to 255
-                maxLength(255)
+                maxLength(MatrixConstants.maxAliasLocalPartLength(data.homeServerName))
                 onFocusChange { hasFocus ->
                     host.aliasTextIsFocused = hasFocus
                 }