diff --git a/gemfiles/rails_4_0.gemfile b/gemfiles/rails_4_0.gemfile
index 65ff419..5fddcc3 100644
--- a/gemfiles/rails_4_0.gemfile
+++ b/gemfiles/rails_4_0.gemfile
@@ -3,6 +3,13 @@ source "https://rubygems.org"
 gem "rails", "~> 4.0.0"
 gem "sqlite3", "~> 1.3.6"
 
+# activesupport uses `BigDecimal#initialize`, but this was removed bigdecimal v1.4.0
+#
+# c.f.
+# * https://github.com/rails/rails/blob/v4.0.13/activesupport/lib/active_support/core_ext/object/duplicable.rb#L82
+# * https://github.com/ruby/bigdecimal/blob/master/CHANGES.md#140
+gem "bigdecimal", "< 1.4.0"
+
 eval_gemfile "#{__dir__}/common.gemfile"
 
 gemspec path: '../'
diff --git a/gemfiles/rails_4_1.gemfile b/gemfiles/rails_4_1.gemfile
index 28a41f9..926525e 100644
--- a/gemfiles/rails_4_1.gemfile
+++ b/gemfiles/rails_4_1.gemfile
@@ -3,6 +3,13 @@ source "https://rubygems.org"
 gem "rails", "~> 4.1.0"
 gem "sqlite3", "~> 1.3.6"
 
+# activesupport uses `BigDecimal#initialize`, but this was removed bigdecimal v1.4.0
+#
+# c.f.
+# * https://github.com/rails/rails/blob/v4.1.16/activesupport/lib/active_support/core_ext/object/duplicable.rb#L82
+# * https://github.com/ruby/bigdecimal/blob/master/CHANGES.md#140
+gem "bigdecimal", "< 1.4.0"
+
 eval_gemfile "#{__dir__}/common.gemfile"
 
 gemspec path: '../'
diff --git a/gemfiles/rails_4_2.gemfile b/gemfiles/rails_4_2.gemfile
index 58b324a..f9a0362 100644
--- a/gemfiles/rails_4_2.gemfile
+++ b/gemfiles/rails_4_2.gemfile
@@ -3,6 +3,13 @@ source "https://rubygems.org"
 gem "rails", "~> 4.2.0"
 gem "sqlite3", "~> 1.3.6"
 
+# activesupport uses `BigDecimal#initialize`, but this was removed bigdecimal v1.4.0
+#
+# c.f.
+# * https://github.com/rails/rails/blob/v4.2.11.3/activesupport/lib/active_support/core_ext/object/duplicable.rb#L111
+# * https://github.com/ruby/bigdecimal/blob/master/CHANGES.md#140
+gem "bigdecimal", "< 1.4.0"
+
 eval_gemfile "#{__dir__}/common.gemfile"
 
 gemspec path: '../'