diff --git a/libbitfury.c b/libbitfury.c
index e5e90e40..51e920a7 100644
--- a/libbitfury.c
+++ b/libbitfury.c
@@ -561,7 +561,11 @@ void libbitfury_sendHashData(struct thr_info *thr, struct bitfury_device *bf, in
 			memcpy(newbuf, spi_getrxbuf() + 4 + chip, 17*4);
 			tm_i2c_clear_oe(slot);
 
-			d->job_switched = (newbuf[16] != oldbuf[16]);
+			if ( 0 == newbuf[16] || 0 == !newbuf[16] )
+             		  d->job_switched = ( newbuf[16] != oldbuf[16]  );
+        		else
+            		  applog(LOG_WARNING, "Unexpected value in newbuf[16] == 0x%08x", newbuf[16]);
+
 
 			d->old_num = 0;
 			d->future_num = 0;