diff --git a/bin/git-effort b/bin/git-effort
index 7d0be16..46e3547 100755
--- a/bin/git-effort
+++ b/bin/git-effort
@@ -4,6 +4,13 @@ tmp=$(git_extra_mktemp)
 above=0
 color=
 
+#
+# print usage message
+#
+usage() {
+  echo 1>&2 "usage: git effort [--above <value>] [<path>...] [-- [<log options>...]]"
+}
+
 #
 # get dates for the given <commit>
 #
@@ -129,6 +136,7 @@ while [ "${#}" -ge 1 ] ; do
       break
       ;;
     --*)
+      usage
       echo 1>&2 "error: unknown argument $1"
       echo 1>&2 "error: if that argument was meant for git-log,"
       echo 1>&2 "error: please put it after two dashes ( -- )."