diff --git a/io_u.c b/io_u.c
index 5971d78..77a3abf 100644
--- a/io_u.c
+++ b/io_u.c
@@ -68,6 +68,9 @@
 	if (td->o.zone_range)
 		max_size = td->o.zone_range;
 
+	if (td->o.min_bs[ddir] > td->o.ba[ddir])
+		max_size -= td->o.min_bs[ddir] - td->o.ba[ddir];
+
 	max_blocks = max_size / (uint64_t) td->o.ba[ddir];
 	if (!max_blocks)
 		return 0;