diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index 8775a4a2c7..8b0ab569d0 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -1076,9 +1076,6 @@ class FormulaInstaller
       #{HOMEBREW_LIBRARY_PATH}/postinstall.rb
     ]
 
-    keg_formula_path = formula.opt_prefix/".brew/#{formula.name}.rb"
-    tap_formula_path = formula.path
-
     # Use the formula from the keg if:
     # * Installing from a local bottle, or
     # * The formula doesn't exist in the tap (or the tap isn't installed), or
@@ -1086,7 +1083,9 @@ class FormulaInstaller
     # In all other cases, including if the formula from the keg is unreadable
     # (third-party taps may `require` some of their own libraries), use the
     # formula from the tap.
-    args << begin
+    formula_path = begin
+      keg_formula_path = formula.opt_prefix/".brew/#{formula.name}.rb"
+      tap_formula_path = formula.path
       keg_formula = Formulary.factory(keg_formula_path)
       tap_formula = Formulary.factory(tap_formula_path) if tap_formula_path.exist?
       other_version_installed = (keg_formula.pkg_version != tap_formula&.pkg_version)
@@ -1102,6 +1101,8 @@ class FormulaInstaller
       tap_formula_path
     end
 
+    args << formula_path
+
     Utils.safe_fork do
       if Sandbox.available?
         sandbox = Sandbox.new