diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index 338bd4771a..9d4b3b4927 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -326,12 +326,11 @@ class FormulaInstaller
   def check_non_libraries
     return unless File.exist? f.lib
 
-    valid_libraries = %w(.a .dylib .framework .jnilib .la .o .so)
-    allowed_non_libraries = %w(.jar .prl .pm)
+    valid_extensions = %w(.a .dylib .framework .jnilib .la .o .so
+                          .jar .prl .pm)
     non_libraries = f.lib.children.select do |g|
       next if g.directory?
-      extname = g.extname
-      (not allowed_non_libraries.include? extname) and (not valid_libraries.include? extname)
+      not valid_extensions.include? g.extname
     end
 
     unless non_libraries.empty?