diff --git a/ext/ftp/ftp.c b/ext/ftp/ftp.c
index 17a3e10e0d61..4b171fd07f18 100644
--- a/ext/ftp/ftp.c
+++ b/ext/ftp/ftp.c
@@ -892,6 +892,11 @@ ftp_get(ftpbuf_t *ftp, php_stream *outstream, const char *path, const size_t pat
 	if (ftp == NULL) {
 		return 0;
 	}
+	if (ftp->in_use) {
+		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
+		return 0;
+	}
+	ftp->in_use = true;
 	if (!ftp_type(ftp, type)) {
 		goto bail;
 	}
@@ -967,9 +972,11 @@ ftp_get(ftpbuf_t *ftp, php_stream *outstream, const char *path, const size_t pat
 		goto bail;
 	}
 
+	ftp->in_use = false;
 	return 1;
 bail:
 	data_close(ftp);
+	ftp->in_use = false;
 	return 0;
 }
 /* }}} */
@@ -1057,6 +1064,11 @@ ftp_put(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *inst
 	if (ftp == NULL) {
 		return 0;
 	}
+	if (ftp->in_use) {
+		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
+		return 0;
+	}
+	ftp->in_use = true;
 	if (!ftp_type(ftp, type)) {
 		goto bail;
 	}
@@ -1097,9 +1109,11 @@ ftp_put(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *inst
 	if (!ftp_getresp(ftp) || (ftp->resp != 226 && ftp->resp != 250 && ftp->resp != 200)) {
 		goto bail;
 	}
+	ftp->in_use = false;
 	return 1;
 bail:
 	data_close(ftp);
+	ftp->in_use = false;
 	return 0;
 }
 /* }}} */
@@ -1114,6 +1128,11 @@ ftp_append(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *i
 	if (ftp == NULL) {
 		return 0;
 	}
+	if (ftp->in_use) {
+		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
+		return 0;
+	}
+	ftp->in_use = true;
 	if (!ftp_type(ftp, type)) {
 		goto bail;
 	}
@@ -1141,9 +1160,11 @@ ftp_append(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *i
 	if (!ftp_getresp(ftp) || (ftp->resp != 226 && ftp->resp != 250 && ftp->resp != 200)) {
 		goto bail;
 	}
+	ftp->in_use = false;
 	return 1;
 bail:
 	data_close(ftp);
+	ftp->in_use = false;
 	return 0;
 }
 /* }}} */
@@ -2223,11 +2244,17 @@ ftp_nb_continue_read(ftpbuf_t *ftp)
 
 	data = ftp->data;
 
+	if (ftp->in_use) {
+		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
+		return PHP_FTP_FAILED;
+	}
+
 	/* check if there is already more data */
 	if (!data_available(ftp, data->fd, false)) {
 		return PHP_FTP_MOREDATA;
 	}
 
+	ftp->in_use = true;
 	type = ftp->type;
 
 	lastch = ftp->lastch;
@@ -2251,6 +2278,7 @@ ftp_nb_continue_read(ftpbuf_t *ftp)
 		}
 
 		ftp->lastch = lastch;
+		ftp->in_use = false;
 		return PHP_FTP_MOREDATA;
 	}
 
@@ -2265,9 +2293,11 @@ ftp_nb_continue_read(ftpbuf_t *ftp)
 	}
 
 	ftp->nb = 0;
+	ftp->in_use = false;
 	return PHP_FTP_FINISHED;
 bail:
 	ftp->nb = 0;
+	ftp->in_use = false;
 	data_close(ftp);
 	return PHP_FTP_FAILED;
 }
@@ -2330,16 +2360,24 @@ ftp_nb_put(ftpbuf_t *ftp, const char *path, const size_t path_len, php_stream *i
 int
 ftp_nb_continue_write(ftpbuf_t *ftp)
 {
+	if (ftp->in_use) {
+		php_error_docref(NULL, E_WARNING, "FTP\\Connection is already in use");
+		return PHP_FTP_FAILED;
+	}
+
 	/* check if we can write more data */
 	if (!data_writeable(ftp, ftp->data->fd)) {
 		return PHP_FTP_MOREDATA;
 	}
 
+	ftp->in_use = true;
+
 	if (ftp_send_stream_to_data_socket(ftp, ftp->data, ftp->stream, ftp->type, true) != SUCCESS) {
 		goto bail;
 	}
 
 	if (!php_stream_eof(ftp->stream)) {
+		ftp->in_use = false;
 		return PHP_FTP_MOREDATA;
 	}
 
@@ -2349,10 +2387,12 @@ ftp_nb_continue_write(ftpbuf_t *ftp)
 		goto bail;
 	}
 	ftp->nb = 0;
+	ftp->in_use = false;
 	return PHP_FTP_FINISHED;
 bail:
 	data_close(ftp);
 	ftp->nb = 0;
+	ftp->in_use = false;
 	return PHP_FTP_FAILED;
 }
 /* }}} */
diff --git a/ext/ftp/ftp.h b/ext/ftp/ftp.h
index 94abc588ca85..91aafad02b79 100644
--- a/ext/ftp/ftp.h
+++ b/ext/ftp/ftp.h
@@ -73,6 +73,7 @@ typedef struct ftpbuf
 	databuf_t		*data;	/* Data connection for "nonblocking" transfers */
 	php_stream		*stream; /* output stream for "nonblocking" transfers */
 	bool			nb;		/* "nonblocking" transfer in progress */
+	bool			in_use;		/* engine transfer in progress; blocks re-entrant ftp_close */
 	char			lastch;		/* last char of previous call */
 	bool			direction;	/* recv = 0 / send = 1 */
 	bool			closestream;/* close or not close stream */
diff --git a/ext/ftp/php_ftp.c b/ext/ftp/php_ftp.c
index 8fa7675c6e9d..f985e5821561 100644
--- a/ext/ftp/php_ftp.c
+++ b/ext/ftp/php_ftp.c
@@ -1220,6 +1220,10 @@ PHP_FUNCTION(ftp_close)
 
 	obj = ftp_object_from_zend_object(Z_OBJ_P(z_ftp));
 	if (obj->ftp) {
+		if (obj->ftp->in_use) {
+			zend_throw_error(NULL, "Cannot close FTP\\Connection while a transfer is in progress");
+			RETURN_THROWS();
+		}
 		success = ftp_quit(obj->ftp);
 		ftp_close(obj->ftp);
 		obj->ftp = NULL;
diff --git a/ext/ftp/tests/ftp_close_during_transfer.phpt b/ext/ftp/tests/ftp_close_during_transfer.phpt
new file mode 100644
index 000000000000..72e410603921
--- /dev/null
+++ b/ext/ftp/tests/ftp_close_during_transfer.phpt
@@ -0,0 +1,44 @@
+--TEST--
+ftp_close() from a stream wrapper during a transfer throws instead of freeing the connection
+--EXTENSIONS--
+ftp
+pcntl
+--FILE--
+<?php
+require 'server.inc';
+
+class CloseDuringWrite {
+    public $context;
+    public static $ftp;
+    public function stream_open($path, $mode, $options, &$opened_path) {
+        return true;
+    }
+    public function stream_write($data) {
+        ftp_close(self::$ftp);
+        return strlen($data);
+    }
+    public function stream_close() {}
+    public function stream_eof() {
+        return true;
+    }
+}
+
+stream_wrapper_register('reentrant', CloseDuringWrite::class);
+
+$ftp = ftp_connect('127.0.0.1', $port);
+var_dump(ftp_login($ftp, 'user', 'pass'));
+CloseDuringWrite::$ftp = $ftp;
+
+try {
+    @ftp_get($ftp, 'reentrant://sink', 'a story.txt', FTP_BINARY);
+} catch (\Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+ftp_close($ftp);
+echo "closed\n";
+?>
+--EXPECT--
+bool(true)
+Cannot close FTP\Connection while a transfer is in progress
+closed
diff --git a/ext/ftp/tests/ftp_nb_close_during_transfer.phpt b/ext/ftp/tests/ftp_nb_close_during_transfer.phpt
new file mode 100644
index 000000000000..702648f69592
--- /dev/null
+++ b/ext/ftp/tests/ftp_nb_close_during_transfer.phpt
@@ -0,0 +1,44 @@
+--TEST--
+ftp_close() from a stream wrapper during a non-blocking transfer throws instead of freeing the connection
+--EXTENSIONS--
+ftp
+pcntl
+--FILE--
+<?php
+require 'server.inc';
+
+class CloseDuringNbWrite {
+    public $context;
+    public static $ftp;
+    public function stream_open($path, $mode, $options, &$opened_path) {
+        return true;
+    }
+    public function stream_write($data) {
+        ftp_close(self::$ftp);
+        return strlen($data);
+    }
+    public function stream_close() {}
+    public function stream_eof() {
+        return true;
+    }
+}
+
+stream_wrapper_register('reentrantnb', CloseDuringNbWrite::class);
+
+$ftp = ftp_connect('127.0.0.1', $port);
+var_dump(ftp_login($ftp, 'user', 'pass'));
+CloseDuringNbWrite::$ftp = $ftp;
+
+try {
+    @ftp_nb_get($ftp, 'reentrantnb://sink', 'a story.txt', FTP_BINARY);
+} catch (\Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+ftp_close($ftp);
+echo "closed\n";
+?>
+--EXPECT--
+bool(true)
+Cannot close FTP\Connection while a transfer is in progress
+closed