diff --git a/src/sao.less b/src/sao.less
index 5f06909e50..aa71e33f19 100644
--- a/src/sao.less
+++ b/src/sao.less
@@ -516,15 +516,15 @@ img.icon {
     .form-multiselection, .form-url, .form-email, .form-callto, .form-sip,
     .form-pyson {
         input, select {
-            min-width: 8em;
+            min-width: 8ch;
         }
     }
     .form-many2one, .form-one2one, .form-reference, form-binary {
         select {
-            min-width: 8em;
+            min-width: 8ch;
         }
         input {
-            min-width: 12em;
+            min-width: 12ch;
         }
     }