diff --git a/middleman-core/lib/middleman-core/preview_server/server_hostname.rb b/middleman-core/lib/middleman-core/preview_server/server_hostname.rb
index 9df133cb..833daa4d 100644
--- a/middleman-core/lib/middleman-core/preview_server/server_hostname.rb
+++ b/middleman-core/lib/middleman-core/preview_server/server_hostname.rb
@@ -3,7 +3,7 @@ module Middleman
     class ServerHostname
       class ServerFullHostname < SimpleDelegator
         def to_s
-          __getobj__
+          __getobj__.gsub(/\s/, '+')
         end
 
         def self.match?(*)
@@ -15,7 +15,7 @@ module Middleman
 
       class ServerPlainHostname < SimpleDelegator
         def to_s
-          __getobj__ + '.local'
+          __getobj__.gsub(/\s/, '+') + '.local'
         end
 
         def self.match?(name)