diff --git a/docs/index.html b/docs/index.html
index f0aebf6..7ebc7dd 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -133,6 +133,17 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
       </div>
     </div>
   </form>
+
+  <div class="form-group">
+    <label>Example of select with <code>.form-control-sm</code></label>
+    <select data-placeholder="Choose one thing" data-allow-clear="1" class="form-control-sm">
+      <option></option>
+      <option>1</option>
+      <option>2</option>
+      <option>3</option>
+    </select>
+  </div>
+
 </div>
 
 <!-- bootstrap -->
diff --git a/src/layout.scss b/src/layout.scss
index f7e193b..a6a5375 100644
--- a/src/layout.scss
+++ b/src/layout.scss
@@ -25,6 +25,17 @@
   border-bottom-right-radius: 0;
 }
 
+// form-control-sm
+.form-control-sm + .select2-container--bootstrap4 {
+  .select2-selection {
+    height: $input-height-sm !important;
+    @include font-size($input-font-size-sm);
+    .select2-selection__rendered {
+      margin-top: -0.2em;
+    }
+  }
+}
+
 .select2-container--bootstrap4 {
 
   // input box