diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 4eaef4b5f65ed..c62896ba00189 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -294,7 +294,7 @@ auto-update() {
     for repo_fetch_head in "${repo_fetch_heads[@]}"
     do
       if [[ ! -f "${repo_fetch_head}" ]] ||
-         [[ -z "$(find "${repo_fetch_head}" -type f -mtime -"${HOMEBREW_AUTO_UPDATE_SECS}"s 2>/dev/null)" ]]
+         [[ -z "$(find "${repo_fetch_head}" -type f -newermt "-${HOMEBREW_AUTO_UPDATE_SECS} seconds" 2>/dev/null)" ]]
       then
         needs_auto_update=1
         break