diff --git a/common/src/comp/player.rs b/common/src/comp/player.rs
index 68818560e4..c713394f72 100644
--- a/common/src/comp/player.rs
+++ b/common/src/comp/player.rs
@@ -1,5 +1,7 @@
 use specs::{Component, FlaggedStorage, NullStorage, VecStorage};
 
+const MAX_ALIAS_LEN: usize = 32;
+
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct Player {
     pub alias: String,
@@ -13,6 +15,11 @@ impl Player {
             view_distance,
         }
     }
+
+    pub fn is_valid(&self) -> bool {
+        self.alias.chars().all(|c| c.is_alphanumeric() || c == '_') && self.alias.len() <= MAX_ALIAS_LEN
+        // TODO: Check view distance here based on server config too
+    }
 }
 
 impl Component for Player {
diff --git a/server/src/lib.rs b/server/src/lib.rs
index aa331e103b..62813a91bb 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -1,4 +1,4 @@
-#![feature(drain_filter)]
+#![feature(drain_filter, bind_by_move_pattern_guards)]
 
 pub mod client;
 pub mod cmd;
@@ -454,7 +454,8 @@ impl Server {
                             ClientState::Dead => client.error_state(RequestStateError::Impossible),
                             ClientState::Pending => {}
                         },
-                        ClientMsg::Register { player } => match client.client_state {
+                        // Valid player
+                        ClientMsg::Register { player } if player.is_valid() => match client.client_state {
                             ClientState::Connected => {
                                 Self::initialize_player(state, entity, client, player);
                                 if let Some(player) =
@@ -467,6 +468,8 @@ impl Server {
                             // Use RequestState instead (No need to send `player` again).
                             _ => client.error_state(RequestStateError::Impossible),
                         },
+                        // Invalid player
+                        ClientMsg::Register { player } => client.error_state(RequestStateError::Impossible),
                         ClientMsg::SetViewDistance(view_distance) => match client.client_state {
                             ClientState::Character { .. } => {
                                 state
diff --git a/voxygen/src/menu/main/mod.rs b/voxygen/src/menu/main/mod.rs
index f2b2ccf505..ecadaa589d 100644
--- a/voxygen/src/menu/main/mod.rs
+++ b/voxygen/src/menu/main/mod.rs
@@ -100,15 +100,22 @@ impl PlayState for MainMenuState {
                         if let Err(err) = global_state.settings.save_to_file() {
                             warn!("Failed to save settings: {:?}", err);
                         }
-                        // Don't try to connect if there is already a connection in progress.
-                        client_init = client_init.or(Some(ClientInit::new(
-                            (server_address, DEFAULT_PORT, false),
-                            comp::Player::new(
-                                username.clone(),
-                                Some(global_state.settings.graphics.view_distance),
-                            ),
-                            false,
-                        )));
+
+                        let player = comp::Player::new(
+                            username.clone(),
+                            Some(global_state.settings.graphics.view_distance),
+                        );
+
+                        if player.is_valid() {
+                            // Don't try to connect if there is already a connection in progress.
+                            client_init = client_init.or(Some(ClientInit::new(
+                                (server_address, DEFAULT_PORT, false),
+                                player,
+                                false,
+                            )));
+                        } else {
+                            self.main_menu_ui.login_error("Invalid username".to_string());
+                        }
                     }
                     MainMenuEvent::StartSingleplayer => {
                         return PlayStateResult::Push(Box::new(StartSingleplayerState::new()));