diff --git a/app/models/user.rb b/app/models/user.rb
index ab6f68b0a..8bf676384 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -38,6 +38,7 @@ class User
   key :visible_person_ids, Array
 
   validates_presence_of :username
+  validates_format_of :username, :without => /\s/
 
   one :person, :class_name => 'Person', :foreign_key => :owner_id
 
diff --git a/config/locales/diaspora/en.yml b/config/locales/diaspora/en.yml
index a2c6a657e..10bfa9070 100644
--- a/config/locales/diaspora/en.yml
+++ b/config/locales/diaspora/en.yml
@@ -12,9 +12,9 @@ en:
               user:
                   attributes:
                       username:
-                          taken: "is already taken."
+                          taken: "is already taken"
                       email:
-                          taken: "is already taken."
+                          taken: "is already taken"
   hello: "Hello world"
   application:
       helper:
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index b239b0f1a..be5986a75 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -52,6 +52,11 @@ describe User do
         user.should be_valid
         user.username.should == "janie"
       end
+
+      it "fails if there's whitespace in the middle" do
+        user = Factory.build(:user, :username => "bobby tables")
+        user.should_not be_valid
+      end
     end
 
     describe "of email" do