diff --git a/RELEASE-NOTES b/RELEASE-NOTES
index 0ad6d9342..0cdf29c31 100644
--- a/RELEASE-NOTES
+++ b/RELEASE-NOTES
@@ -87,6 +87,7 @@ This release includes the following bugfixes:
  o telnet: Fix typos [45]
  o transfer: only retry nobody-requests for HTTP [46]
  o http2: reset push header counter fixes crash [47]
+ o nss: make FTPS work with --proxytunnel [48]
 
 This release includes the following known bugs:
 
@@ -157,3 +158,4 @@ References to bug reports and discussions on issues:
  [45] = https://curl.haxx.se/bug/?i=1245
  [46] = https://curl.haxx.se/bug/?i=1243
  [47] = https://curl.haxx.se/bug/?i=1249
+ [48] = https://bugzilla.redhat.com/1420327
diff --git a/lib/vtls/nss.c b/lib/vtls/nss.c
index aefe636eb..d5158acef 100644
--- a/lib/vtls/nss.c
+++ b/lib/vtls/nss.c
@@ -1612,13 +1612,14 @@ static CURLcode nss_fail_connect(struct ssl_connect_data *connssl,
   return curlerr;
 }
 
-/* Switch the SSL socket into non-blocking mode. */
-static CURLcode nss_set_nonblock(struct ssl_connect_data *connssl,
-                                 struct Curl_easy *data)
+/* Switch the SSL socket into blocking or non-blocking mode. */
+static CURLcode nss_set_blocking(struct ssl_connect_data *connssl,
+                                 struct Curl_easy *data,
+                                 bool blocking)
 {
   static PRSocketOptionData sock_opt;
   sock_opt.option = PR_SockOpt_Nonblocking;
-  sock_opt.value.non_blocking = PR_TRUE;
+  sock_opt.value.non_blocking = !blocking;
 
   if(PR_SetSocketOption(connssl->handle, &sock_opt) != PR_SUCCESS)
     return nss_fail_connect(connssl, data, CURLE_SSL_CONNECT_ERROR);
@@ -2007,16 +2008,14 @@ static CURLcode nss_connect_common(struct connectdata *conn, int sockindex,
       /* we do not expect CURLE_AGAIN from nss_setup_connect() */
       return result;
 
-    if(!blocking) {
-      /* in non-blocking mode, set NSS non-blocking mode before handshake */
-      result = nss_set_nonblock(connssl, data);
-      if(result)
-        return result;
-    }
-
     connssl->connecting_state = ssl_connect_2;
   }
 
+  /* enable/disable blocking mode before handshake */
+  result = nss_set_blocking(connssl, data, blocking);
+  if(result)
+    return result;
+
   result = nss_do_connect(conn, sockindex);
   switch(result) {
   case CURLE_OK:
@@ -2032,7 +2031,7 @@ static CURLcode nss_connect_common(struct connectdata *conn, int sockindex,
 
   if(blocking) {
     /* in blocking mode, set NSS non-blocking mode _after_ SSL handshake */
-    result = nss_set_nonblock(connssl, data);
+    result = nss_set_blocking(connssl, data, /* blocking */ FALSE);
     if(result)
       return result;
   }