diff --git a/browsermob-proxy.gemspec b/browsermob-proxy.gemspec
index 0859e5a..9c086b2 100644
--- a/browsermob-proxy.gemspec
+++ b/browsermob-proxy.gemspec
@@ -16,7 +16,7 @@ Gem::Specification.new do |s|
   s.rubyforge_project = "browsermob-proxy-rb"
 
   s.add_runtime_dependency "rest-client"
-  s.add_runtime_dependency "childprocess", "~> 0.5"
+  s.add_runtime_dependency "childprocess", ">= 0.5", "< 4.0"
   s.add_runtime_dependency "multi_json", "~> 1.0"
   s.add_runtime_dependency "har"