diff --git a/NEWS b/NEWS
index 48afd654b2ef..4ea6485c80e2 100644
--- a/NEWS
+++ b/NEWS
@@ -51,6 +51,8 @@ PHP                                                                        NEWS
 
 - FTP:
   . Fix double free in ext/ftp data_accept() on accept failure. (alepacheco)
+  . Fixed ftp_nb_put() not aborting a pending non-blocking transfer, which
+    leaked its data connection. (Jakub Kozub)
 
 - MBString:
   . Fixed bug GH-23958 (truncated encoding names resolving to full names). (Kamil Tekiela)
diff --git a/ext/ftp/ftp.c b/ext/ftp/ftp.c
index fd0f295500b8..7bfe4c69c26a 100644
--- a/ext/ftp/ftp.c
+++ b/ext/ftp/ftp.c
@@ -2329,6 +2329,14 @@ ftp_nb_put(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *i
 		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
 		return PHP_FTP_FAILED;
 	}
+	if (ftp->data != NULL) {
+		/* If there is a transfer in action, abort it.
+		 * If we don't, we get an invalid state and memory leaks when the new connection gets opened. */
+		data_close(ftp);
+		if (!ftp_getresp(ftp) || (ftp->resp != 226 && ftp->resp != 250)) {
+			goto bail;
+		}
+	}
 	if (!ftp_type(ftp, type)) {
 		goto bail;
 	}
diff --git a/ext/ftp/tests/ftp_nb_put_during_nb_transfer.phpt b/ext/ftp/tests/ftp_nb_put_during_nb_transfer.phpt
new file mode 100644
index 000000000000..ca7968813fe5
--- /dev/null
+++ b/ext/ftp/tests/ftp_nb_put_during_nb_transfer.phpt
@@ -0,0 +1,42 @@
+--TEST--
+ftp_nb_put() must abort a pending non-blocking transfer, like ftp_nb_get() does
+--EXTENSIONS--
+ftp
+pcntl
+--FILE--
+<?php
+require 'server.inc';
+
+$ftp = ftp_connect('127.0.0.1', $port);
+if (!$ftp) die("Couldn't connect to the server");
+var_dump(ftp_login($ftp, 'user', 'pass'));
+
+$local_file = __DIR__ . DIRECTORY_SEPARATOR . "ftp_nb_put_during_nb_transfer.txt";
+$fout = fopen($local_file, "w");
+
+/* Requests more data, but we deliberately do not loop to fetch it, so a
+ * transfer is still pending when the upload below starts. */
+var_dump(ftp_nb_fget($ftp, $fout, "fget", FTP_BINARY, 0) === FTP_MOREDATA);
+fclose($fout);
+
+/* Without the guard in ftp_nb_put() this reuses ftp->data while the previous
+ * databuf_t is still owned by it, and reads the pending transfer's response
+ * as the answer to its own command. */
+$ret = ftp_nb_put($ftp, basename(__FILE__), __FILE__, FTP_ASCII);
+while ($ret == FTP_MOREDATA) {
+    $ret = ftp_nb_continue($ftp);
+}
+var_dump($ret === FTP_FINISHED);
+
+ftp_close($ftp);
+echo "closed\n";
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . DIRECTORY_SEPARATOR . "ftp_nb_put_during_nb_transfer.txt");
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+closed