diff --git a/src/common/tortls.c b/src/common/tortls.c
index 7f601258c4..51c4abe247 100644
--- a/src/common/tortls.c
+++ b/src/common/tortls.c
@@ -850,7 +850,14 @@ tor_tls_get_pending_bytes(tor_tls_t *tls)
     return 0;
 #endif
   return SSL_pending(tls->ssl);
+}
 
+/** If <b>tls</b> requires that the next write be of a particular size,
+ * return that size.  Otherwise, return 0. */
+size_t
+tor_tls_get_forced_write_size(tor_tls_t *tls)
+{
+  return tls->wantwrite_n;
 }
 
 /** Return the number of bytes read across the underlying socket. */
diff --git a/src/common/tortls.h b/src/common/tortls.h
index 2569abf79c..dea072a338 100644
--- a/src/common/tortls.h
+++ b/src/common/tortls.h
@@ -41,6 +41,7 @@ int tor_tls_write(tor_tls_t *tls, char *cp, size_t n);
 int tor_tls_handshake(tor_tls_t *tls);
 int tor_tls_shutdown(tor_tls_t *tls);
 int tor_tls_get_pending_bytes(tor_tls_t *tls);
+size_t tor_tls_get_forced_write_size(tor_tls_t *tls);
 
 unsigned long tor_tls_get_n_bytes_read(tor_tls_t *tls);
 unsigned long tor_tls_get_n_bytes_written(tor_tls_t *tls);
diff --git a/src/or/buffers.c b/src/or/buffers.c
index 55120c60a7..aeca8b0ec3 100644
--- a/src/or/buffers.c
+++ b/src/or/buffers.c
@@ -648,16 +648,21 @@ flush_buf(int s, buf_t *buf, size_t sz, size_t *buf_flushlen)
   return flushed;
 }
 
-/** Helper for flush_buf_tls(): try to write <b>sz</b> bytes from buffer
- * <b>buf</b> onto TLS object <b>tls</b>.  On success, deduct the bytes
- * written from *<b>buf_flushlen</b>.
- * Return the number of bytes written on success, -1 on failure.
+/** Helper for flush_buf_tls(): try to write <b>sz</b> bytes (or more if
+ * required by a previous write) from buffer <b>buf</b> onto TLS object
+ * <b>tls</b>.  On success, deduct the bytes written from
+ * *<b>buf_flushlen</b>.  Return the number of bytes written on success, -1 on
+ * failure.
  */
 static INLINE int
 flush_buf_tls_impl(tor_tls_t *tls, buf_t *buf, size_t sz, size_t *buf_flushlen)
 {
   int r;
+  size_t forced;
 
+  forced = tor_tls_get_forced_write_size(tls);
+  if (forced < sz)
+    sz = forced;
   r = tor_tls_write(tls, buf->cur, sz);
   if (r < 0) {
     return r;