diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index aeca22d91101..f0ecd98509d8 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -201,7 +201,20 @@ static struct kmem_cache *bfq_pool;
 /* Target observation time interval for a peak-rate update (ns) */
 #define BFQ_RATE_REF_INTERVAL	NSEC_PER_SEC
 
-/* Shift used for peak rate fixed precision calculations. */
+/*
+ * Shift used for peak-rate fixed precision calculations.
+ * With
+ * - the current shift: 16 positions
+ * - the current type used to store rate: u32
+ * - the current unit of measure for rate: [sectors/usec], or, more precisely,
+ *   [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
+ * the range of rates that can be stored is
+ * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
+ * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
+ * [15, 65G] sectors/sec
+ * Which, assuming a sector size of 512B, corresponds to a range of
+ * [7.5K, 33T] B/sec
+ */
 #define BFQ_RATE_SHIFT		16
 
 /*
@@ -2637,6 +2650,16 @@ static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
 	rate /= divisor; /* smoothing constant alpha = 1/divisor */
 
 	bfqd->peak_rate += rate;
+
+	/*
+	 * For a very slow device, bfqd->peak_rate can reach 0 (see
+	 * the minimum representable values reported in the comments
+	 * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
+	 * divisions by zero where bfqd->peak_rate is used as a
+	 * divisor.
+	 */
+	bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
+
 	update_thr_responsiveness_params(bfqd);
 
 reset_computation:
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 350c39ae2896..ae2f3dadec44 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -499,7 +499,7 @@ struct bfq_data {
 	u64 delta_from_first;
 	/*
 	 * Current estimate of the device peak rate, measured in
-	 * [BFQ_RATE_SHIFT * sectors/usec]. The left-shift by
+	 * [(sectors/usec) / 2^BFQ_RATE_SHIFT]. The left-shift by
 	 * BFQ_RATE_SHIFT is performed to increase precision in
 	 * fixed-point calculations.
 	 */