diff --git a/check_curl.sh b/check_curl.sh
index de12195..4d38c14 100755
--- a/check_curl.sh
+++ b/check_curl.sh
@@ -443,7 +443,7 @@ fi
 BODY_CONTAINS=""
 if [ -n "$CRIT_STRING" ]; then
   BODY=$(curl -s $FOLLOW_REDIRECTS $INSECURE $HEADERS $RESOLVE $TIMEOUT $AUTHENTICATION "$URL")
-  if ! [[ $BODY =~ $CRIT_STRING ]]; then
+    if ! echo "$BODY" | grep -Fq "$CRIT_STRING"; then
       if $SANITIZE_HTML; then
         BODY=$(echo "$BODY" | sed 's/</\&lt;/g' | sed 's/>/\&gt;/g')
       fi