diff --git a/clang-format.bash b/clang-format.bash
index 53b7216..c41269c 100755
--- a/clang-format.bash
+++ b/clang-format.bash
@@ -1,11 +1,11 @@
 #! /usr/bin/env bash
 
-shopt -s globstar
+shopt -s extglob globstar
 
 # Switch to the directory containing the script so that relative paths may be
 # used.
 cd "${0%/*}"
-files=(**/*.c **/*.cc **/*.h)
+files=(!(build)/**/*.c **/*.cc **/*.h)
 if [ "$1" = check ]
 then
     clang-format --verbose --dry-run -Werror ${files[@]}