diff --git a/.ruby-version b/.ruby-version
new file mode 100644
index 0000000..37c2961
--- /dev/null
+++ b/.ruby-version
@@ -0,0 +1 @@
+2.7.2
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..5d7c324 100644
--- a/test/slug_test.rb
+++ b/test/slug_test.rb
@@ -28,6 +28,11 @@
       assert_equal(orphan.id.to_s, query)
     end
 
+    it "does not modify the source column" do
+      article = Article.create(headline: 'A long, complex, headline')
+      assert_equal('A long, complex, headline', article.headline)
+    end
+
     describe "slug column" do
       it "saves slug to 'slug' column by default" do
         article = Article.create!(:headline => 'Test Headline')