diff --git a/src/engine/tw-font-manager.js b/src/engine/tw-font-manager.js
index 1535aa04bf3..f617a67f95e 100644
--- a/src/engine/tw-font-manager.js
+++ b/src/engine/tw-font-manager.js
@@ -22,6 +22,22 @@ const log = require('../util/log');
  */
 const removeInvalidCharacters = font => font.replace(/[^-\w ]/g, '');
 
+/**
+ * @param {InternalFont[]} fonts Modified in-place
+ * @param {InternalFont} newFont
+ * @returns {InternalFont|null}
+ */
+const addOrUpdateFont = (fonts, newFont) => {
+    let oldFont;
+    const oldIndex = fonts.findIndex(i => i.family.toLowerCase() === newFont.family.toLowerCase());
+    if (oldIndex !== -1) {
+        oldFont = fonts[oldIndex];
+        fonts.splice(oldIndex, 1);
+    }
+    fonts.push(newFont);
+    return oldFont;
+};
+
 class FontManager extends EventEmitter {
     /**
      * @param {Runtime} runtime
@@ -129,11 +145,14 @@ class FontManager extends EventEmitter {
         if (!this.isValidSystemFont(family)) {
             throw new Error('Invalid system font family');
         }
-        this.fonts.push({
+        const oldFont = addOrUpdateFont(this.fonts, {
             system: true,
             family,
             fallback
         });
+        if (oldFont && !oldFont.system) {
+            this.updateRenderer();
+        }
         this.changed();
     }
 
@@ -146,14 +165,12 @@ class FontManager extends EventEmitter {
         if (!this.isValidCustomFont(family)) {
             throw new Error('Invalid custom font family');
         }
-
-        this.fonts.push({
+        addOrUpdateFont(this.fonts, {
             system: false,
             family,
             fallback,
             asset
         });
-
         this.updateRenderer();
         this.changed();
     }
diff --git a/test/integration/tw_font_manager.js b/test/integration/tw_font_manager.js
index a9cc635b852..452fabc687a 100644
--- a/test/integration/tw_font_manager.js
+++ b/test/integration/tw_font_manager.js
@@ -714,3 +714,53 @@ test('restrict removes existing fonts', t => {
 
     t.end();
 });
+
+test('overriding existing fonts', t => {
+    let setCustomFontsCalls = 0;
+    const mockRenderer = {
+        setLayerGroupOrdering: () => {},
+        setCustomFonts: () => {
+            setCustomFontsCalls++;
+        }
+    };
+
+    const rt = new Runtime();
+    rt.attachRenderer(mockRenderer);
+    rt.attachStorage(makeTestStorage());
+    const {fontManager, storage} = rt;
+
+    let changeEvents = 0;
+    fontManager.on('change', () => {
+        changeEvents++;
+    });
+
+    const asset = storage.createAsset(
+        storage.AssetType.Font,
+        'ttf',
+        new Uint8Array([11, 12, 13]),
+        null,
+        true
+    );
+
+    fontManager.addCustomFont('TestFont', 'sans-serif', asset);
+    t.equal(changeEvents, 1);
+    t.equal(setCustomFontsCalls, 1);
+    t.same(fontManager.getFonts().map(i => i.name), ['TestFont']);
+
+    fontManager.addSystemFont('TestFonT', 'sans-serif');
+    t.equal(changeEvents, 2);
+    t.equal(setCustomFontsCalls, 2);
+    t.same(fontManager.getFonts().map(i => i.name), ['TestFonT']);
+
+    fontManager.addSystemFont('TestFONT', 'sans-serif');
+    t.equal(changeEvents, 3);
+    t.equal(setCustomFontsCalls, 2);
+    t.same(fontManager.getFonts().map(i => i.name), ['TestFONT']);
+
+    fontManager.addCustomFont('TESTFONT', 'sans-serif', asset);
+    t.equal(changeEvents, 4);
+    t.equal(setCustomFontsCalls, 3);
+    t.same(fontManager.getFonts().map(i => i.name), ['TESTFONT']);
+
+    t.end();
+});