diff --git a/bin/brew b/bin/brew
index 8668b69e73..527a8d39e4 100755
--- a/bin/brew
+++ b/bin/brew
@@ -71,8 +71,9 @@ end
 def dump_build_env env
   puts "\"--use-llvm\" was specified" if ARGV.include? '--use-llvm'
 
-  %w[CC CXX LD CFLAGS CPPFLAGS CXXFLAGS LDFLAGS MAKEFLAGS PKG_CONFIG_PATH HOMEBREW_USE_LLVM].each do |k|
-    puts "#{k}: #{env[k]}"
+  %w[CC CXX LD CFLAGS CXXFLAGS CPPFLAGS LDFLAGS MAKEFLAGS PKG_CONFIG_PATH HOMEBREW_USE_LLVM].each do |k|
+    value = env[k]
+    puts "#{k}: #{value}" if value
   end
 end