diff --git a/tools/offline/scripts/update_downloads.sh b/tools/offline/scripts/update_downloads.sh
index 247b92e562..28cd267c27 100755
--- a/tools/offline/scripts/update_downloads.sh
+++ b/tools/offline/scripts/update_downloads.sh
@@ -14,11 +14,41 @@ function update_setting()
   sed -i "/^$1=/c$1=\"$2\"" init_http_cache.sh
 }
 
+DETECTED_URLS=$(grep -PoRh "\w+_URL" ../../../cmake/ | sort | uniq | grep -v ^LAMMPS)
+KNOWN_URLS=$(grep -Rh "_URL=" init_http_cache.sh | grep -v ^LAMMPS | grep -v SCAFACOS_FIX | cut -d= -f1)
 
-URLS=$(grep -Rh "_URL=" init_http_cache.sh | grep -v ^LAMMPS | grep -v SCAFACOS_FIX | cut -d= -f1)
+# check if init_http_cache.sh contains all URLs
+for URL in $DETECTED_URLS
+do
+  grep -q ^$URL= init_http_cache.sh
+  if [ $? -ne 0 ]
+  then
+    FILENAME_VAR="${URL/_URL/_FILENAME}"
+    echo $URL is not known. Please update 'init_http_cache.sh' as follows:
+    echo
+    echo 1. add the following line:
+    echo
+    echo $URL=""
+    echo
+    echo 2. Define a new $FILENAME_VAR if necessary
+    echo
+    echo $FILENAME_VAR="pkgname-0.0.0.tar.gz"
+    echo
+    echo 3. extend TARBALLS with $URL
+    echo
+    echo TARBALLS=\(
+    echo "    ..."
+    echo "    $URL"
+    echo \)
+    echo
+    echo 4. Rerun this script
+    echo
+    exit 1
+  fi
+done
 
 # update URLs by grabbing the latest ones from cmake files
-for URL in $URLS
+for URL in $KNOWN_URLS
 do
   extract_setting "$URL"
   update_setting "$URL" ${!URL}