diff --git a/crawler/extract-image-urls.sh b/crawler/extract-image-urls.sh
index da07574755..508f45f42b 100755
--- a/crawler/extract-image-urls.sh
+++ b/crawler/extract-image-urls.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 set -e -u -x
 
-grep --ignore-case --only-matching --no-filename '<img[^/]*src=\"[^">]*"' -r --include=*.opt . \
+grep --ignore-case --only-matching --no-filename --mmap '<img[^/]*src=\"[^">]*"' -r --include=*.opt . \
   | sed 's/<img.*src="//g' \
   | sed 's/"$//g' \
   | sort -u \