diff --git a/README.md b/README.md
index 003dd7c..480441d 100644
--- a/README.md
+++ b/README.md
@@ -55,6 +55,9 @@ this article: [How to: Change / Setup bash custom prompt (PS1)][how-to]
 
 [how-to]: http://www.cyberciti.biz/tips/howto-linux-unix-bash-shell-setup-prompt.html
 
+If you don't want untracked files to be included in the "dirty" decision process,
+set the variable `GIT_PROMPT_IGNORE_UNTRACKED` to any value.
+
 
 ### Suggested Prompts
 
diff --git a/prompt.sh b/prompt.sh
index 6a737b8..de15137 100644
--- a/prompt.sh
+++ b/prompt.sh
@@ -12,7 +12,7 @@ find_git_branch() {
 }
 
 find_git_dirty() {
-  local status=$(git status --porcelain 2> /dev/null)
+  local status=$(git status --porcelain ${GIT_PROMPT_IGNORE_UNTRACKED:+--untracked-files=no} 2> /dev/null)
   if [[ "$status" != "" ]]; then
     git_dirty='*'
   else