diff --git a/git-getpull b/git-getpull
index d0c426e..e8657d3 100644
--- a/git-getpull
+++ b/git-getpull
@@ -1,6 +1,9 @@
 #!/bin/sh
 
-if [ -z "$(git rev-parse --git-dir 2>/dev/null)" ]; then
+if [ -z "$1" ]; then
+  echo "Usage: git getpull <SHA>"
+  exit 1
+elif [ -z "$(git rev-parse --git-dir 2>/dev/null)" ]; then
   echo "Not in a git directory"
   exit 1
 else