diff --git a/activerecord-crate-adapter.gemspec b/activerecord-crate-adapter.gemspec
index df18ca3..7106aff 100644
--- a/activerecord-crate-adapter.gemspec
+++ b/activerecord-crate-adapter.gemspec
@@ -52,5 +52,5 @@ Gem::Specification.new do |spec|
   spec.add_dependency('arel', '>= 5.0.0')
   spec.add_dependency('crate_ruby', '~> 0.2.0')
   # https://github.com/ruby/bigdecimal#which-version-should-you-select
-  spec.add_dependency('bigdecimal', '~> 1.4')
+  spec.add_dependency('bigdecimal', '>= 1.4', '< 4.0')
 end