diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index 92023028eb..6d9c0b938e 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -180,7 +180,7 @@ class FormulaInstaller
     build_bottle_preinstall if build_bottle?
 
     unless @poured_bottle
-      if formula.file_modified?
+      if formula.file_modified? && !build_from_source?
         filename = formula.path.to_s.gsub("#{HOMEBREW_PREFIX}/", "")
         opoo "Formula file is modified!"
         puts "Building from source because #{filename} has local changes"