diff --git a/ssh_filter_btrbk.sh b/ssh_filter_btrbk.sh
index 5cd9c6e..6d9c415 100755
--- a/ssh_filter_btrbk.sh
+++ b/ssh_filter_btrbk.sh
@@ -41,7 +41,7 @@ reject_and_die()
 {
     local reason="$1"
     log_cmd 'auth.err' 'btrbk REJECT' "$reason"
-    echo "ERROR: ssh_filter_btrbk.sh: ssh command rejected: $reason: $SSH_ORIGINAL_COMMAND" 1>&2
+    printf 'ERROR: ssh_filter_btrbk.sh: ssh command rejected: %s: %s\n' "$reason" "$SSH_ORIGINAL_COMMAND" 1>&2
     exit 255
 }
 
@@ -165,7 +165,7 @@ while [ "$#" -ge 1 ]; do
           ;;
 
       *)
-          echo "ERROR: ssh_filter_btrbk.sh: failed to parse command line option: $key" 1>&2
+          printf 'ERROR: ssh_filter_btrbk.sh: failed to parse command line option: %s\n' "$key" 1>&2
           exit 255
           ;;
     esac