diff --git a/Library/Homebrew/requirement.rb b/Library/Homebrew/requirement.rb
index 9540f09675..d4da0255a0 100644
--- a/Library/Homebrew/requirement.rb
+++ b/Library/Homebrew/requirement.rb
@@ -43,8 +43,10 @@ class Requirement
 
   # Overriding #modify_build_environment is deprecated.
   # Pass a block to the the env DSL method instead.
+  # Note: #satisfied? should be called before invoking this method
+  # as the env modifications may depend on its side effects.
   def modify_build_environment
-    satisfied? and env.modify_build_environment(self)
+    env.modify_build_environment(self)
   end
 
   def env
diff --git a/Library/Homebrew/test/test_requirement.rb b/Library/Homebrew/test/test_requirement.rb
index 5d89defb05..042aa922df 100644
--- a/Library/Homebrew/test/test_requirement.rb
+++ b/Library/Homebrew/test/test_requirement.rb
@@ -81,6 +81,7 @@ class RequirementTests < Test::Unit::TestCase
     ENV.expects(:userpaths!)
     ENV.expects(:append).with("PATH", which_path.parent, ":")
 
+    req.satisfied?
     req.modify_build_environment
   end