diff --git a/client_test.go b/client_test.go
index a713556..161dc11 100644
--- a/client_test.go
+++ b/client_test.go
@@ -96,6 +96,19 @@ func testConn(t *testing.T, disableEPSV bool) {
 		r.Close()
 	}
 
+	fileSize, err := c.FileSize("tset")
+	if err != nil {
+		t.Error(err)
+	}
+	if fileSize != 14 {
+		t.Errorf("file size %q, expected %q", fileSize, 14)
+	}
+
+	fileSize, err = c.FileSize("not-found")
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+
 	err = c.Delete("tset")
 	if err != nil {
 		t.Error(err)
diff --git a/ftp.go b/ftp.go
index 219d987..03dd7c7 100644
--- a/ftp.go
+++ b/ftp.go
@@ -408,13 +408,13 @@ func (c *ServerConn) CurrentDir() (string, error) {
 }
 
 // FileSize issues a SIZE FTP command, which Returns the size of the file
-func (c *ServerConn) FileSize(path string) (int, error) {
+func (c *ServerConn) FileSize(path string) (int64, error) {
 	_, msg, err := c.cmd(StatusFile, "SIZE %s", path)
 	if err != nil {
 		return 0, err
 	}
 
-	size, err := strconv.Atoi(msg)
+	size, err := strconv.ParseInt(msg, 10, 64)
 	if err != nil {
 		return 0, err
 	}