diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index 4672b31..625d6e8 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -113,6 +113,11 @@
         max-width: var(--content-width, 80ch);
         min-width: var(--content-width, 80ch);
       }
+      .content,
+      .lineNum {
+        /* Set font size based the user's diff preference. */
+        font-size: var(--font-size, 12px);
+      }
       .content.add .intraline,
       .content.add.darkHighlight {
         background-color: var(--dark-add-highlight-color);
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
index 1a6759b..e876dc0 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
@@ -359,6 +359,7 @@
     _prefsChanged: function(prefs) {
       if (!prefs) { return; }
       this.customStyle['--content-width'] = prefs.line_length + 'ch';
+      this.customStyle['--font-size'] = prefs.font_size + 'px';
       this.updateStyles();
 
       if (this._diff && this._comments) {