diff --git a/sms.fnl b/sms.fnl
index 431bdb3..68e4b46 100644
--- a/sms.fnl
+++ b/sms.fnl
@@ -33,16 +33,22 @@
 ;(print (escape-for-logging (unicode-to-gsm "{he@llo}€")))
 
 
-(fn expect [fd pattern]
+(fn expect [fd pattern fail-pattern]
   (let [b (read fd 1024)]
     (if (> (# b) 0)
         (do
           (print (.. "<<< " (escape-for-logging b)))
           (if (string.find b pattern)
               (do (print "found" pattern) true)
+              (and fail-pattern (string.find b fail-pattern))
+              (error (.. "Expected " pattern ", got " (escape-for-logging b)))
               (expect fd pattern)))
         nil)))
 
+(fn command [fd s]
+  (tx fd (.. s "\r\n"))
+  (expect fd "OK" "ERROR"))
+
 (fn send-sms [number body]
   (let [fd (fcntl.open "/dev/serial/by-id/usb-HUAWEI_HUAWEI_HiLink-if00-port0" posix.O_RDWR)
         termios (tcgetattr fd)]
@@ -54,33 +60,17 @@
                                (bnot ISIG)))
     (tset termios :oflag (band termios.oflag ( bnot OPOST)))
     (tcsetattr fd 0 termios)
-    ;; opt->c_cc[VMIN]  = 1;
-    ;; opt->c_cc[VTIME] = 10;
+
     (tcdrain fd)
     (doto fd
-      (tx  "AT\r\n")
-      (expect "OK")
-
-      (tx  "AT&F\r\n")
-      (expect "OK")
-
-      (tx  "ATE0\r\n")                  ;disable command echo
-      (expect "OK")
-
-      (tx "AT+CMEE=1\r\n")              ;print CME errors
-      (expect "OK")
-
-      (tx "AT+CMGF=1\r\n")              ;SMS text mode (not PDU mode)
-      (expect "OK")
-
-      (tx "AT+CSCS=\"GSM\"\r\n")        ; default character set
-      (expect "OK")
-
-      (tx "AT+CSMP=17,12,0,0\r\n")      ; message valid for 12*5 minutes
-      (expect "OK")
-
-      (tx "AT+CSCA=\"+447958879879\",145\r\n") ;set SMSC
-      (expect "OK")
+      (command "AT")
+      (command "AT&F")                  ; revert to defaults
+      (command "ATE0")                  ; disable command echo
+      (command "AT+CMEE=1")              ;print CME errors
+      (command "AT+CMGF=1")              ;SMS text mode (vs. PDU mode)
+      (command "AT+CSCS=\"GSM\"")        ; default character set
+      (command "AT+CSMP=17,12,0,0")      ; message valid for 12*5 minutes
+      (command "AT+CSCA=\"+447958879879\",145\r\n") ;set SMSC
 
       (tx (.. "AT+CMGS=\"" number "\"\r\n"))
       (expect ">")