diff --git a/net/rds/ib_send.c b/net/rds/ib_send.c
index 71f373c421bc4d8b6a97f2be7201a2dc8c2290e8..c47a511f203d463d70eea98bc594ae7468bf9919 100644
--- a/net/rds/ib_send.c
+++ b/net/rds/ib_send.c
@@ -551,7 +551,10 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 	if (conn->c_loopback
 	    && rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
 		rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
-		return sizeof(struct rds_header) + RDS_CONG_MAP_BYTES;
+		scat = &rm->data.op_sg[sg];
+		ret = sizeof(struct rds_header) + RDS_CONG_MAP_BYTES;
+		ret = min_t(int, ret, scat->length - conn->c_xmit_data_off);
+		return ret;
 	}
 
 	/* FIXME we may overallocate here */
diff --git a/net/rds/loop.c b/net/rds/loop.c
index aeec1d483b17e6f65c858e1510c7752965e35260..bca6761a3ca2f578b1355e670dbb446ad24cd20a 100644
--- a/net/rds/loop.c
+++ b/net/rds/loop.c
@@ -61,10 +61,15 @@ static int rds_loop_xmit(struct rds_connection *conn, struct rds_message *rm,
 			 unsigned int hdr_off, unsigned int sg,
 			 unsigned int off)
 {
+	struct scatterlist *sgp = &rm->data.op_sg[sg];
+	int ret = sizeof(struct rds_header) +
+			be32_to_cpu(rm->m_inc.i_hdr.h_len);
+
 	/* Do not send cong updates to loopback */
 	if (rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
 		rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
-		return sizeof(struct rds_header) + RDS_CONG_MAP_BYTES;
+		ret = min_t(int, ret, sgp->length - conn->c_xmit_data_off);
+		goto out;
 	}
 
 	BUG_ON(hdr_off || sg || off);
@@ -80,8 +85,8 @@ static int rds_loop_xmit(struct rds_connection *conn, struct rds_message *rm,
 			    NULL);
 
 	rds_inc_put(&rm->m_inc);
-
-	return sizeof(struct rds_header) + be32_to_cpu(rm->m_inc.i_hdr.h_len);
+out:
+	return ret;
 }
 
 /*