diff --git a/plugins/libcalendaring/libcalendaring.php b/plugins/libcalendaring/libcalendaring.php
index e33edbdc..0f769b93 100644
--- a/plugins/libcalendaring/libcalendaring.php
+++ b/plugins/libcalendaring/libcalendaring.php
@@ -432,6 +432,12 @@ class libcalendaring extends rcube_plugin
             foreach ($m2 as $seg) {
                 $prefix = $seg[2] == 'D' || $seg[2] == 'W' ? 'P' : 'PT';
                 if ($seg[1] > 0) {  // ignore zero values
+                    // convert seconds to minutes
+                    if ($seg[2] == 'S') {
+                        $seg[2] = 'M';
+                        $seg[1] = round($seg[1]/60);
+                    }
+
                     return array($seg[1], $m[1].$seg[2], $m[1].$seg[1].$seg[2], $m[1].$prefix.$seg[1].$seg[2]);
                 }
             }