diff --git a/auto-update b/auto-update
index 9278302..b190ee8 100755
--- a/auto-update
+++ b/auto-update
@@ -1,9 +1,6 @@
 #!/usr/bin/env sh
 
-note() {
-    local IFS=' '
-    printf '\033[1m%s\033[0m\n' "$*" >&2
-}
+note() { printf >&2 '\033[1m%s\033[0m\n' "$*" ;}
 
 investigate() {
     url="${1?huh}"
@@ -12,6 +9,9 @@ investigate() {
     curl $curlflags "$url" | grep -F "$re" | grep -Eo '[0-9a-f]{40}'
 }
 
+me="$(readlink -f "$0")" && cd "${me%/*}" || exit
+curlflags="-L --no-progress-meter"
+any=0
 set -- \
 cosmo           COSMO_COMMIT    https://github.com/jart/cosmopolitan \
 cosmo-kuroko    KUROKO_COMMIT   https://github.com/kuroko-lang/kuroko \
@@ -22,27 +22,27 @@ cosmo-yices     KISSAT_COMMIT   https://github.com/BrunoDutertre/kissat \
 cosmo-yices     YICES_COMMIT    https://github.com/SRI-CSL/yices2 \
 ;
 
-me="$(readlink -f "$0")" && cd "${me%/*}" || exit
-curlflags="-L --no-progress-meter"
-any=0
-
 while [ $# != 0 ]; do
     dir="$1" tag="$2" url="$3"
     shift && shift && shift || { note 'not a multiple of 3!'; exit 255 ;}
+    if ! [ -d "$dir" -a -f "$dir/Dockerfile" -a -s "$dir/Dockerfile" ]; then
+        note "missing Dockerfile, skipping $dir ($tag)"
+        continue
+    fi
     ours="$(grep -F "$tag"= "$dir/Dockerfile" | grep -Eo '[0-9a-f]{40}' | head -n1)"
     theirs="$(investigate "$url" | head -n1)"
-    if [ ${#theirs} == 0 ]; then
-        note "failed to retrieve update for $tag"
+    if [ ${#ours} == 0 -o ${#theirs} == 0 ]; then
+        note "failed to retrieve update for $dir ($tag)"
     elif [ "$ours" != "$theirs" ]; then
-        any=1
-        note "updating $dir"
+        any=1 && note "updating $dir ($tag)"
         other="${tag%_COMMIT}_SHA256"
-        tgz="${url%/}"
-        tgz="${tgz%%/tree/*}"
-        tgz="$tgz/archive/$theirs.tar.gz"
-        sum="$(curl $curlflags "$tgz" | sha256sum - | awk '{print $1}')"
-        notwa-util/shed "$dir/Dockerfile" "s/$ours/$theirs/g"
-        notwa-util/shed "$dir/Dockerfile" "s/$other=.*/$other=$sum/g"
+        tgz="${url%/}" && tgz="${tgz%%/tree/*}" && tgz="$tgz/archive/$theirs.tar.gz"
+        { : \
+         && sum="$(curl $curlflags "$tgz" | sha256sum - | awk '{print $1}')" \
+         && notwa-util/shed "$dir/Dockerfile" "s/$ours/$theirs/g" \
+         && notwa-util/shed "$dir/Dockerfile" "s/$other=.*/$other=$sum/g" \
+         ;} \
+     || note "failed to apply update for $dir ($tag)"
     fi
 done
 [ $any = 1 ] || note "no new updates"