diff --git a/lib/slug/slug.rb b/lib/slug/slug.rb
index 23aa38e..51695ee 100644
--- a/lib/slug/slug.rb
+++ b/lib/slug/slug.rb
@@ -48,7 +48,7 @@ def set_slug(opts={})
       validate_slug_columns
       return if self[self.slug_column].present? && !opts[:force]
 
-      self[self.slug_column] = normalize_slug(self.send(self.slug_source))
+      self[self.slug_column] = normalize_slug(self.send(self.slug_source).dup)
 
       # if normalize_slug returned a blank string, try the generic_default handling
       if generic_default && self[self.slug_column].blank?
diff --git a/test/slug_test.rb b/test/slug_test.rb
index 607587a..21dd583 100644
--- a/test/slug_test.rb
+++ b/test/slug_test.rb
@@ -179,6 +179,13 @@
       assert_match 'abc', @article.slug
     end
 
+    it "does not spoil the value" do
+      @article.headline = 'abc!@#$%^&*•¶§∞¢££¡¿()><?""\':;][]\.,/'
+      headline = @article.headline.dup
+      @article.save!
+      assert_match headline, @article.headline
+    end
+
     it "strips trailing space" do
       @article.headline = 'ab '
       @article.save!