diff --git a/addons/mail/static/src/less/composer.less b/addons/mail/static/src/less/composer.less
index 9213fb6c416..a22a626c584 100644
--- a/addons/mail/static/src/less/composer.less
+++ b/addons/mail/static/src/less/composer.less
@@ -136,7 +136,7 @@
 
         &.o_chat_inline_composer {
             .o_composer_container {
-                .o-flex(1, 0, auto);
+                .o-flex(1, 1, auto);
             }
             .o_composer {
                 padding: @o-mail-chatter-gap @o-mail-chatter-gap 0 @o-mail-chatter-gap;