diff --git a/web/toolbar.js b/web/toolbar.js
index 5aa1313b1..af8bc2158 100644
--- a/web/toolbar.js
+++ b/web/toolbar.js
@@ -17,7 +17,6 @@ import {
   animationStarted,
   DEFAULT_SCALE,
   DEFAULT_SCALE_VALUE,
-  docStyle,
   MAX_SCALE,
   MIN_SCALE,
   noContextMenuHandler,
@@ -342,7 +341,8 @@ class Toolbar {
     maxWidth += 0.3 * scaleSelectWidth;
 
     if (maxWidth > scaleSelectWidth) {
-      docStyle.setProperty("--scale-select-width", `${maxWidth}px`);
+      const container = items.scaleSelect.parentNode;
+      container.style.setProperty("--scale-select-width", `${maxWidth}px`);
     }
     // Zeroing the width and height cause Firefox to release graphics resources
     // immediately, which can greatly reduce memory consumption.
diff --git a/web/viewer.css b/web/viewer.css
index 3a79aa4f2..68842a724 100644
--- a/web/viewer.css
+++ b/web/viewer.css
@@ -20,7 +20,6 @@
   --sidebar-width: 200px;
   --sidebar-transition-duration: 200ms;
   --sidebar-transition-timing-function: ease;
-  --scale-select-width: 140px;
 
   --toolbar-icon-opacity: 0.7;
   --doorhanger-icon-opacity: 0.9;
@@ -799,6 +798,10 @@ body {
 }
 
 .dropdownToolbarButton {
+  /* Define this variable here, and not in :root, to avoid reflowing the
+     entire viewer when updating the width. */
+  --scale-select-width: 140px;
+
   width: var(--scale-select-width);
   padding: 0;
   background-color: var(--dropdown-btn-bg-color);