diff --git a/app/logical/tag_name_validator.rb b/app/logical/tag_name_validator.rb
new file mode 100644
index 000000000..872b9861d
--- /dev/null
+++ b/app/logical/tag_name_validator.rb
@@ -0,0 +1,30 @@
+class TagNameValidator < ActiveModel::EachValidator
+  def validate_each(record, attribute, value)
+    case Tag.normalize_name(value)
+    when /\A_*\z/
+      record.errors[attribute] << "'#{value}' cannot be blank"
+    when /\*/
+      record.errors[attribute] << "'#{value}' cannot contain asterisks ('*')"
+    when /,/
+      record.errors[attribute] << "'#{value}' cannot contain commas (',')"
+    when /\A~/
+      record.errors[attribute] << "'#{value}' cannot begin with a tilde ('~')"
+    when /\A-/
+      record.errors[attribute] << "'#{value}' cannot begin with a dash ('-')"
+    when /\A_/
+      record.errors[attribute] << "'#{value}' cannot begin with an underscore"
+    when /_\z/
+      record.errors[attribute] << "'#{value}' cannot end with an underscore"
+    when /__/
+      record.errors[attribute] << "'#{value}' cannot contain consecutive underscores"
+    when /[^[[:graph:]]]/
+      record.errors[attribute] << "'#{value}' cannot contain non-printable characters"
+    when /[^[[:ascii:]]]/
+      record.errors[attribute] << "'#{value}' must consist of only ASCII characters"
+    when /\A(#{Tag::METATAGS}|#{Tag::SUBQUERY_METATAGS}):(.+)\z/i
+      record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
+    when /\A(#{Tag.categories.regexp}):(.+)\z/i
+      record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
+    end
+  end
+end
diff --git a/app/models/tag.rb b/app/models/tag.rb
index 445c001f2..301b89f1b 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -6,6 +6,8 @@ class Tag < ActiveRecord::Base
   attr_accessible :is_locked, :as => [:moderator, :admin]
   has_one :wiki_page, :foreign_key => "title", :primary_key => "name"
 
+  validates :name, uniqueness: true, tag_name: true, on: :create
+
   module ApiMethods
     def to_legacy_json
       return {
@@ -179,7 +181,7 @@ class Tag < ActiveRecord::Base
 
   module NameMethods
     def normalize_name(name)
-      name.mb_chars.downcase.tr(" ", "_").gsub(/\A[-~]+/, "").gsub(/\*/, "").to_s
+      name.to_s.mb_chars.downcase.strip.tr(" ", "_").to_s
     end
 
     def find_or_create_by_name(name, options = {})