diff --git a/Gemfile.lock b/Gemfile.lock
index 8233cc7..642a7a2 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: .
   specs:
     mailinator (1.0.0)
-      hashie (>= 3.5.4, < 3.7.0)
+      hashie (>= 3.5.4, < 4.1.0)
 
 GEM
   remote: https://rubygems.org/
@@ -35,7 +35,7 @@ GEM
       guard (~> 2.1)
       guard-compat (~> 1.1)
       rspec (>= 2.99.0, < 4.0)
-    hashie (3.6.0)
+    hashie (4.0.0)
     jaro_winkler (1.5.2)
     json (2.1.0)
     listen (3.1.5)
diff --git a/mailinator.gemspec b/mailinator.gemspec
index c30e705..257b0b2 100644
--- a/mailinator.gemspec
+++ b/mailinator.gemspec
@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ['lib']
 
-  spec.add_dependency 'hashie', '>= 3.5.4', '< 3.7.0'
+  spec.add_dependency 'hashie', '>= 3.5.4', '< 4.1.0'
 
   spec.add_development_dependency 'bundler', '~> 1.16.2'
   spec.add_development_dependency 'rake', '~> 12.3.1'