diff --git a/middleman-core/middleman-core-x86-mingw32.gemspec b/middleman-core/middleman-core-x86-mingw32.gemspec
index d1779828..1ec32454 100644
--- a/middleman-core/middleman-core-x86-mingw32.gemspec
+++ b/middleman-core/middleman-core-x86-mingw32.gemspec
@@ -27,7 +27,7 @@ Gem::Specification.new do |s|
   s.add_dependency("rack-test", ["~> 0.6.1"])
   
   # CLI
-  s.add_dependency("thor", ["~> 0.15.4"])
+  s.add_dependency("thor", [">= 0.15.4", "~> 0.15"])
   
   # Helpers
   s.add_dependency("activesupport", ["~> 3.2.6"])
diff --git a/middleman-core/middleman-core.gemspec b/middleman-core/middleman-core.gemspec
index c366daa3..4eb1aed0 100644
--- a/middleman-core/middleman-core.gemspec
+++ b/middleman-core/middleman-core.gemspec
@@ -26,7 +26,7 @@ Gem::Specification.new do |s|
   s.add_dependency("rack-test", ["~> 0.6.1"])
   
   # CLI
-  s.add_dependency("thor", ["~> 0.15.4"])
+  s.add_dependency("thor", [">= 0.15.4", "~> 0.15"])
   
   # Helpers
   s.add_dependency("activesupport", ["~> 3.2.6"])