diff --git a/crypto/bio/bss_dgram_pair.c b/crypto/bio/bss_dgram_pair.c
index 534a2216aa..08dd802d8f 100644
--- a/crypto/bio/bss_dgram_pair.c
+++ b/crypto/bio/bss_dgram_pair.c
@@ -279,8 +279,9 @@ static int dgram_pair_init(BIO *bio)
     if (b == NULL)
         return 0;
 
-    b->req_buf_len = 17*1024; /* default buffer size */
     b->mtu         = 1472;    /* conservative default MTU */
+    /* default buffer size */
+    b->req_buf_len = 9 * (sizeof(struct dgram_hdr) + b->mtu);
 
     b->lock = CRYPTO_THREAD_lock_new();
     if (b->lock == NULL) {
diff --git a/test/bio_dgram_test.c b/test/bio_dgram_test.c
index f6c3e30c14..70157493f9 100644
--- a/test/bio_dgram_test.c
+++ b/test/bio_dgram_test.c
@@ -559,8 +559,11 @@ static int test_bio_dgram_pair(int idx)
         goto err;
 
     /*
-     * Should be able to fit at least 9 datagrams in default write buffer size
-     * in worst case
+     * The number of datagrams we can fit depends on the size of the default
+     * write buffer size, the size of the datagram header and the size of the
+     * payload data we send in each datagram. The max payload data is based on
+     * the mtu. The default write buffer size is 9 * (sizeof(header) + mtu) so
+     * we expect at least 9 maximally sized datagrams to fit in the buffer.
      */
     if (!TEST_int_ge(i, 9))
         goto err;