diff --git a/ChangeLog.md b/ChangeLog.md
index e857bbc8..cac08500 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,9 @@
+### 0.3.10 / TBA
+
+#### auto.sh
+
+* Preserve the value of `$_` for `bash` users. (@HaleTom)
+
 ### 0.3.9 / 2014-11-23
 
 #### chruby.sh
diff --git a/share/chruby/auto.sh b/share/chruby/auto.sh
index 88f3cb34..1fe60767 100644
--- a/share/chruby/auto.sh
+++ b/share/chruby/auto.sh
@@ -2,6 +2,7 @@ unset RUBY_AUTO_VERSION
 
 function chruby_auto() {
 	local dir="$PWD/" version
+	local old_="$1" # Save $_ for bash users
 
 	until [[ -z "$dir" ]]; do
 		dir="${dir%/*}"
@@ -22,6 +23,7 @@ function chruby_auto() {
 		chruby_reset
 		unset RUBY_AUTO_VERSION
 	fi
+	: "$old_" # restore $_ (last argument of last command executed)
 }
 
 if [[ -n "$ZSH_VERSION" ]]; then
@@ -29,5 +31,5 @@ if [[ -n "$ZSH_VERSION" ]]; then
 		preexec_functions+=("chruby_auto")
 	fi
 elif [[ -n "$BASH_VERSION" ]]; then
-	trap '[[ "$BASH_COMMAND" != "$PROMPT_COMMAND" ]] && chruby_auto' DEBUG
+	trap '[[ "$BASH_COMMAND" != "$PROMPT_COMMAND" ]] && chruby_auto "$_"' DEBUG
 fi
diff --git a/test/unit/chruby_auto_test.sh b/test/unit/chruby_auto_test.sh
index 3011f38e..832a325d 100755
--- a/test/unit/chruby_auto_test.sh
+++ b/test/unit/chruby_auto_test.sh
@@ -157,6 +157,11 @@ function test_chruby_auto_ruby_version_containing_options()
 		     "$expected_auto_version" "$RUBY_AUTO_VERSION"
 }
 
+function test_chruby_auto_preserves_dollar_underscore() {
+	: foo # Run a null command to set $_ to "foo"
+	assertEquals "value of $_ does not change" "$_" "foo"
+}
+
 function tearDown()
 {
 	cd "$original_pwd"