diff --git a/bundler/lib/bundler/spec_set.rb b/bundler/lib/bundler/spec_set.rb
index a19d18388ab8..44715c356743 100644
--- a/bundler/lib/bundler/spec_set.rb
+++ b/bundler/lib/bundler/spec_set.rb
@@ -24,7 +24,7 @@ def for(dependencies, check = false, match_current_platform = false)
 
         specs_for_dep = spec_for_dependency(dep, match_current_platform)
         if specs_for_dep.any?
-          match_current_platform ? specs += specs_for_dep : specs |= specs_for_dep
+          specs.concat(specs_for_dep)
 
           specs_for_dep.first.dependencies.each do |d|
             next if d.type == :development
@@ -40,6 +40,8 @@ def for(dependencies, check = false, match_current_platform = false)
         specs << spec
       end
 
+      specs.uniq! unless match_current_platform
+
       check ? true : specs
     end