diff --git a/theme/boost/scss/moodle/forms.scss b/theme/boost/scss/moodle/forms.scss
index 3ad2675b31a..e618cce1060 100644
--- a/theme/boost/scss/moodle/forms.scss
+++ b/theme/boost/scss/moodle/forms.scss
@@ -22,6 +22,13 @@
     margin-bottom: 4px;
 }
 
+.mform .form-inline {
+    .form-control,
+    .custom-select {
+        max-width: 100%;
+    }
+}
+
 .mform fieldset {
     margin-left: $spacer * 1.5;
     margin-bottom: $spacer / 2;