diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index d7d8cba014697602832fe20e414b632104c9f239..749a428824371a27473a4715e33d97d691cdfc97 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -444,7 +444,8 @@ static inline int sctp_frag_point(const struct sctp_association *asoc, int pmtu)
 	if (asoc->user_frag)
 		frag = min_t(int, frag, asoc->user_frag);
 
-	frag = SCTP_TRUNC4(min_t(int, frag, SCTP_MAX_CHUNK_LEN));
+	frag = SCTP_TRUNC4(min_t(int, frag, SCTP_MAX_CHUNK_LEN -
+					    sizeof(struct sctp_data_chunk)));
 
 	return frag;
 }
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 4c0a772927924c34abe7ffc03e7b295da7041068..3204a9b294071db44c9de0e503e1bd5d7cd6f52b 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3140,9 +3140,9 @@ static int sctp_setsockopt_mappedv4(struct sock *sk, char __user *optval, unsign
  */
 static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned int optlen)
 {
+	struct sctp_sock *sp = sctp_sk(sk);
 	struct sctp_assoc_value params;
 	struct sctp_association *asoc;
-	struct sctp_sock *sp = sctp_sk(sk);
 	int val;
 
 	if (optlen == sizeof(int)) {
@@ -3158,26 +3158,35 @@ static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned
 		if (copy_from_user(&params, optval, optlen))
 			return -EFAULT;
 		val = params.assoc_value;
-	} else
+	} else {
 		return -EINVAL;
+	}
 
-	if ((val != 0) && ((val < 8) || (val > SCTP_MAX_CHUNK_LEN)))
-		return -EINVAL;
+	if (val) {
+		int min_len, max_len;
 
-	asoc = sctp_id2assoc(sk, params.assoc_id);
-	if (!asoc && params.assoc_id && sctp_style(sk, UDP))
-		return -EINVAL;
+		min_len = SCTP_DEFAULT_MINSEGMENT - sp->pf->af->net_header_len;
+		min_len -= sizeof(struct sctphdr) +
+			   sizeof(struct sctp_data_chunk);
+
+		max_len = SCTP_MAX_CHUNK_LEN - sizeof(struct sctp_data_chunk);
 
+		if (val < min_len || val > max_len)
+			return -EINVAL;
+	}
+
+	asoc = sctp_id2assoc(sk, params.assoc_id);
 	if (asoc) {
 		if (val == 0) {
-			val = asoc->pathmtu;
-			val -= sp->pf->af->net_header_len;
+			val = asoc->pathmtu - sp->pf->af->net_header_len;
 			val -= sizeof(struct sctphdr) +
-					sizeof(struct sctp_data_chunk);
+			       sizeof(struct sctp_data_chunk);
 		}
 		asoc->user_frag = val;
 		asoc->frag_point = sctp_frag_point(asoc, asoc->pathmtu);
 	} else {
+		if (params.assoc_id && sctp_style(sk, UDP))
+			return -EINVAL;
 		sp->user_frag = val;
 	}