diff --git a/src/cheerios.c b/src/cheerios.c
index 6d27b0e..5ab880f 100644
--- a/src/cheerios.c
+++ b/src/cheerios.c
@@ -216,17 +216,18 @@ cheerios_insert(const char *buf, size_t len)
 
 
 static void
-__xmodem_callback(size_t sent, size_t total)
+__xmodem_callback(size_t sent, size_t total, int ack_fails)
 {
     char status_str[1024];
 
 
     snprintf(
         status_str, sizeof(status_str),
-        "\r  %.02f/%.02fKB (%.01f%%)",
+        "\r  %.02f/%.02fKB (%.01f%%, %d ACK fails)",
         (sent / 1024.0),
         (total / 1024.0),
-        (sent * 100.0 / total)
+        (sent * 100.0 / total),
+        ack_fails
     );
 
     cheerios_insert(status_str, strlen(status_str));
diff --git a/src/xmodem.c b/src/xmodem.c
index 8edc8e9..9bf850d 100644
--- a/src/xmodem.c
+++ b/src/xmodem.c
@@ -20,7 +20,7 @@ xmodem_send(
     int in_fd,
     size_t sz,
     int block_sz,
-    void (*status_cb)(size_t sent, size_t total)
+    void (*status_cb)(size_t sent, size_t total, int ack_fails)
 )
 {
     uint8_t start_byte;
@@ -30,6 +30,7 @@ xmodem_send(
     uint8_t packet_num;
     int retries;
     int ret = 0;
+    int ack_fails = 0;
 
     if (block_sz != 128 && block_sz != 1024) {
         return -1;
@@ -120,11 +121,12 @@ xmodem_send(
             }
 
             retries++;
+            ack_fails++;
         }
 
         sent += read_len;
         packet_num++; /* expect overflow */
-        status_cb(sent, sz);
+        status_cb(sent, sz, ack_fails);
     }
 
 end_of_transmission:
diff --git a/src/xmodem.h b/src/xmodem.h
index ecc0092..ac65b02 100644
--- a/src/xmodem.h
+++ b/src/xmodem.h
@@ -34,7 +34,7 @@ int xmodem_send(
     int in_fd,
     size_t sz,
     int block_sz,
-    void (*status_cb)(size_t sent, size_t total)
+    void (*status_cb)(size_t sent, size_t total, int ack_fails)
 );
 
 #if 0