diff --git a/Library/Homebrew/extend/ENV/shared.rb b/Library/Homebrew/extend/ENV/shared.rb
index 27df5793d9..03e6364033 100644
--- a/Library/Homebrew/extend/ENV/shared.rb
+++ b/Library/Homebrew/extend/ENV/shared.rb
@@ -64,11 +64,11 @@ module SharedEnvExtension
   end
 
   def cc= val
-    self['CC'] = self['OBJC'] = val
+    self['CC'] = self['OBJC'] = val.to_s
   end
 
   def cxx= val
-    self['CXX'] = self['OBJCXX'] = val
+    self['CXX'] = self['OBJCXX'] = val.to_s
   end
 
   def cc;       self['CC'];           end