diff --git a/theme/boost/scss/moodle/forms.scss b/theme/boost/scss/moodle/forms.scss
index df3cdcb18a9..7194c865ecf 100644
--- a/theme/boost/scss/moodle/forms.scss
+++ b/theme/boost/scss/moodle/forms.scss
@@ -296,9 +296,14 @@ fieldset.coursesearchbox label {
     font-size: large;
 }
 
+/* Non-bootstrap selects with a size show their contents outside of the element. Remove when we update to stable bootstrap 4. */
+select[size],
 select[multiple] {
     overflow: auto;
 }
+select[size=1] {
+    overflow: visible;
+}
 
 textarea[data-auto-rows] {
     overflow-x: hidden;