diff --git a/CHANGELOG.md b/CHANGELOG.md
index d4dc24aa7..1f218308a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@ Bugfixes:
 
   - Use #underscore, not #downcase for help text scope (#140, @atipugin)
   - Radio button and checkbox labels will now include the disabled class as needed. (#156, @ScottSwezey)
+  - Can't override primary button classes (#183, @tanimichi)
 
 Features:
 
diff --git a/lib/bootstrap_form/helpers/bootstrap.rb b/lib/bootstrap_form/helpers/bootstrap.rb
index 0dac054b6..44bc6d816 100644
--- a/lib/bootstrap_form/helpers/bootstrap.rb
+++ b/lib/bootstrap_form/helpers/bootstrap.rb
@@ -2,12 +2,12 @@ module BootstrapForm
   module Helpers
     module Bootstrap
       def submit(name = nil, options = {})
-        options.merge! class: 'btn btn-default' unless options.has_key? :class
+        options.reverse_merge! class: 'btn btn-default'
         super(name, options)
       end
 
       def primary(name = nil, options = {})
-        options.merge! class: 'btn btn-primary'
+        options.reverse_merge! class: 'btn btn-primary'
         submit(name, options)
       end
 
diff --git a/test/bootstrap_other_components_test.rb b/test/bootstrap_other_components_test.rb
index 5b2258100..b86fb9d63 100644
--- a/test/bootstrap_other_components_test.rb
+++ b/test/bootstrap_other_components_test.rb
@@ -51,4 +51,9 @@ def setup
     expected = %{<input class="btn btn-primary" name="commit" type="submit" value="Submit Form" />}
     assert_equal expected, @builder.primary("Submit Form")
   end
+
+  test "override primary button classes" do
+    expected = %{<input class="btn btn-primary disabled" name="commit" type="submit" value="Submit Form" />}
+    assert_equal expected, @builder.primary("Submit Form", class: "btn btn-primary disabled")
+  end
 end