diff --git a/lib/grep.zsh b/lib/grep.zsh
index 348ebe623..9a2c6f5a3 100644
--- a/lib/grep.zsh
+++ b/lib/grep.zsh
@@ -1,24 +1,25 @@
-# is x grep argument available?
-grep-flag-available() {
-    echo | grep $1 "" >/dev/null 2>&1
-}
-
-# color grep results
-GREP_OPTIONS="--color=auto"
-
-# ignore VCS folders (if the necessary grep flags are available)
+# Ignore VCS folders (if the necessary grep flags are available).
 VCS_FOLDERS="{.bzr,.cvs,.git,.hg,.svn}"
 
-if grep-flag-available --exclude-dir=.cvs; then
-    GREP_OPTIONS+=" --exclude-dir=$VCS_FOLDERS"
-elif grep-flag-available --exclude=.cvs; then
-    GREP_OPTIONS+=" --exclude=$VCS_FOLDERS"
-fi
+_setup_grep_alias() {
+    # Is grep argument $1 available?
+    grep-flag-available() {
+        echo | grep $1 "" >/dev/null 2>&1
+    }
 
-# export grep settings
-alias grep="grep $GREP_OPTIONS"
+    # Color grep results.
+    local GREP_OPTIONS="--color=auto"
 
-# clean up
-unset GREP_OPTIONS
-unset VCS_FOLDERS
-unfunction grep-flag-available
+    if grep-flag-available --exclude-dir=.cvs; then
+        GREP_OPTIONS+=" --exclude-dir=$VCS_FOLDERS"
+    elif grep-flag-available --exclude=.cvs; then
+        GREP_OPTIONS+=" --exclude=$VCS_FOLDERS"
+    fi
+
+    # Re-define alias.
+    alias grep="grep $GREP_OPTIONS"
+
+    # Clean up.
+    unfunction grep-flag-available
+}
+alias grep=_setup_grep_alias