diff --git a/Gemfile.lock b/Gemfile.lock
index 4f48f1a..d113b35 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,7 +6,7 @@ PATH
       block_logger (~> 0.1)
       digest-sha3 (~> 1.1)
       ethash (~> 0.2)
-      ffi (>= 1.9.10)
+      ffi (~> 1.9.10)
       lru_redux (~> 1.1)
       rlp (~> 0.6)
 
diff --git a/ruby-ethereum.gemspec b/ruby-ethereum.gemspec
index 3340f36..712bce1 100644
--- a/ruby-ethereum.gemspec
+++ b/ruby-ethereum.gemspec
@@ -18,13 +18,13 @@ Gem::Specification.new do |s|
   s.add_dependency('ethash', '~> 0.2')
   s.add_dependency('bitcoin-secp256k1', '~> 0.3')
   s.add_dependency('lru_redux', '~> 1.1')
-  s.add_dependency('ffi', '>= 1.9.10')
+  s.add_dependency('ffi', '~> 1.9')
   s.add_dependency('digest-sha3', '~> 1.1')
   s.add_dependency('block_logger', '~> 0.1')
 
   s.add_development_dependency('rake', '~> 10.5')
   s.add_development_dependency('minitest', '5.8.3')
   s.add_development_dependency('yard', '0.8.7.6')
-  s.add_development_dependency('serpent', '>= 0.3.0')
-  s.add_development_dependency('pry-byebug', '>= 2.0.0')
+  s.add_development_dependency('serpent', '~> 0.3')
+  s.add_development_dependency('pry-byebug', '~> 2.0')
 end