diff --git a/lib/gel/gemfile_parser.rb b/lib/gel/gemfile_parser.rb
index 44ced05..c35beb5 100644
--- a/lib/gel/gemfile_parser.rb
+++ b/lib/gel/gemfile_parser.rb
@@ -143,13 +143,21 @@ def initialize(filename)
     def flatten(options, stack)
       options = options.dup
       stack.reverse_each do |layer|
-        options.update(layer) { |_, current, outer| current }
+        options.update(layer) { |_, current, outer| Array(outer) + Array(current) }
       end
+
       @git_sources.each do |key, block|
         next unless options.key?(key)
         raise "Multiple git sources specified" if options.key?(:git)
         options[:git] = block.call(options.delete(key))
       end
+
+      if options[:install_if]
+        options[:install_if] = Array(options[:install_if]).all? do |condition|
+          condition.respond_to?(:call) ? condition.call : condition
+        end
+      end
+
       options
     end
 
@@ -158,12 +166,6 @@ def add_gem(name, requirements, options)
       raise "Only git sources can specify a :branch" if options[:branch] && !options[:git]
       raise "Duplicate entry for gem #{name.inspect}" if @gems.assoc(name)
 
-      if options[:install_if]
-        options[:install_if] = Array(options[:install_if]).all? do |condition|
-          condition.respond_to?(:call) ? condition.call : condition
-        end
-      end
-
       @gems << [name, requirements, options]
     end
 
diff --git a/test/gemfile_parser_test.rb b/test/gemfile_parser_test.rb
index 96b7d80..6503ae8 100644
--- a/test/gemfile_parser_test.rb
+++ b/test/gemfile_parser_test.rb
@@ -19,11 +19,11 @@ class GemfileParserTest < Minitest::Test
 end
 
 group :test do
-  gem "minitest-bisect"
+  gem "minitest-bisect", group: :development
 
   platforms :mri do
     gem "stackprof"
-    gem "byebug"
+    gem "byebug", platforms: :rbx
   end
 
   gem "benchmark-ips"
@@ -42,10 +42,10 @@ def test_simple_parse
       ["rake", [">= 11.1"], {}],
       ["mocha", [], require: false],
       ["bcrypt", ["~> 3.1.11"], require: false],
-      ["w3c_validators", [], group: [:doc], require: "w3c_validators/validator"],
-      ["minitest-bisect", [], group: [:test]],
+      ["w3c_validators", [], require: "w3c_validators/validator", group: [:doc]],
+      ["minitest-bisect", [], group: [:test, :development]],
       ["stackprof", [], platforms: [:mri], group: [:test]],
-      ["byebug", [], platforms: [:mri], group: [:test]],
+      ["byebug", [], platforms: [:mri, :rbx], group: [:test]],
       ["benchmark-ips", [], group: [:test]],
       ["rails-assets-bootstrap", [], source: "https://rails-assets.org"],
     ], result.gems
@@ -149,8 +149,8 @@ def test_install_if
   gem "activesupport", "2.3.5"
 end
 gem "thin", :install_if => lambda { false }
-install_if lambda { false } do
-  gem "foo"
+install_if true, lambda { nil } do
+  gem "foo", :install_if => true
 end
 gem "bar", :install_if => [true, lambda { 1 }]
 gem "rack"