diff --git a/share/man/man9/bus_dma.9 b/share/man/man9/bus_dma.9
index 22213686b113..124e2583b53e 100644
--- a/share/man/man9/bus_dma.9
+++ b/share/man/man9/bus_dma.9
@@ -322,7 +322,8 @@ Boundary constraint, in bytes, of the target DMA memory region.
 The boundary indicates the set of addresses, all multiples of the
 boundary argument, that cannot be crossed by a single
 .Vt bus_dma_segment_t .
-The boundary must be a power of 2.
+The boundary must be a power of 2 and must be no smaller that the
+maximum segment size.
 .Ql 0
 indicates that there are no boundary restrictions.
 .It Fa lowaddr