diff --git a/cfg_checker/modules/network/mapper.py b/cfg_checker/modules/network/mapper.py
index 59f3781..483c11f 100644
--- a/cfg_checker/modules/network/mapper.py
+++ b/cfg_checker/modules/network/mapper.py
@@ -395,7 +395,8 @@
                 for idx_y in range(m):
                     line = ""
                     for idx_x in range(n):
-                        _fmt = "{" + ":{}".format(_columns[idx_x]) + "} "
+                        _len = _columns[idx_x] if _columns[idx_x] else 1
+                        _fmt = "{" + ":{}".format(_len) + "} "
                         line += _fmt.format(matrix[idx_x][idx_y])
                     lines.append(line)
                 node_data['networks'][_ifname]['matrix'] = matrix