diff --git a/update_depot_tools b/update_depot_tools
index ce95e8857d..76ebf191ae 100755
--- a/update_depot_tools
+++ b/update_depot_tools
@@ -130,6 +130,9 @@ if [ "X$DEPOT_TOOLS_UPDATE" != "X0" ]; then
     cd "$base_dir"
     update_git_repo
     cd - > /dev/null
+  else
+    echo "Warning: Your depot_tools directory does not appear to be a git repository, and cannot be updated." 1>&2
+    echo "Consider deleting your depot_tools directory and following the instructions at https://www.chromium.org/developers/how-tos/install-depot-tools/ to reinstall it." 1>&2
   fi
 
   # Sync CIPD-boostrapped packages.