diff --git a/Gemfile.lock b/Gemfile.lock
index 781a283..dc8561a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -2,18 +2,16 @@ PATH
   remote: .
   specs:
     mixmax (0.1.5)
-      httparty (~> 0.16.4)
+      httparty (>= 0.16.4, < 0.22.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
     diff-lcs (1.3)
-    httparty (0.16.4)
-      mime-types (~> 3.0)
+    httparty (0.21.0)
+      mini_mime (>= 1.0.0)
       multi_xml (>= 0.5.2)
-    mime-types (3.2.2)
-      mime-types-data (~> 3.2015)
-    mime-types-data (3.2019.0331)
+    mini_mime (1.1.2)
     multi_xml (0.6.0)
     rake (10.5.0)
     rspec (3.8.0)
diff --git a/mixmax.gemspec b/mixmax.gemspec
index 1b99b24..f984202 100644
--- a/mixmax.gemspec
+++ b/mixmax.gemspec
@@ -23,5 +23,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "rspec", "~> 3.0"
 
-  spec.add_dependency "httparty", "~> 0.16.4"
+  spec.add_dependency "httparty", ">= 0.16.4", "< 0.22.0"
 end