diff --git a/package-lock.json b/package-lock.json
index 47d1a7a..63c6e0c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,7 +10,7 @@
       "license": "MIT",
       "dependencies": {
         "@makeitaquote/utils": "^1.2.1",
-        "@napi-rs/canvas": "^1.0.8",
+        "@napi-rs/canvas": ">=1.0.8 <1.0.12",
         "@twemoji/parser": "^17.0.2",
         "budoux": "^0.9.1",
         "cleye": "^2.6.0",
diff --git a/package.json b/package.json
index 3a75b76..61fee7e 100644
--- a/package.json
+++ b/package.json
@@ -74,7 +74,7 @@
   },
   "dependencies": {
     "@makeitaquote/utils": "^1.2.1",
-    "@napi-rs/canvas": "^1.0.8",
+    "@napi-rs/canvas": ">=1.0.8 <1.0.12",
     "@twemoji/parser": "^17.0.2",
     "budoux": "^0.9.1",
     "cleye": "^2.6.0",
diff --git a/src/render/avatar.ts b/src/render/avatar.ts
index f6ecb77..ca8a41e 100644
--- a/src/render/avatar.ts
+++ b/src/render/avatar.ts
@@ -6,6 +6,7 @@ import type { AvatarTheme } from '../theme/types'
 import type { AssetCache } from '../util/assetCache'
 import { avatarCache } from './avatarCache'
 import { createCanvas, type Image, loadImage, type SKRSContext2D } from './canvasFactory'
+import { fontString } from './layout'
 
 const http = createClient({ timeout: 15_000, retry: 2 })
 
@@ -261,7 +262,7 @@ export function drawAvatar(
     if (initial) {
       const size = Math.min(box.width, box.height) * 0.22
       ctx.fillStyle = toCSS(parseColor(theme.fallback.color, 'theme.avatar.fallback.color'))
-      ctx.font = `${size}px ${options.fallbackFont ?? 'sans-serif'}`
+      ctx.font = fontString('normal', size, options.fallbackFont ?? 'sans-serif')
       ctx.textAlign = 'center'
       ctx.textBaseline = 'middle'
       ctx.fillText(initial.toUpperCase(), box.x + box.width / 2, box.y + box.height / 2)
diff --git a/src/render/layout.test.ts b/src/render/layout.test.ts
index 98e86db..54327c1 100644
--- a/src/render/layout.test.ts
+++ b/src/render/layout.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 import { defineTheme } from '../theme/resolve'
-import { autoArea, computeLayout, fontString, gradientLine } from './layout'
+import { autoArea, computeLayout, cssFontFamily, fontString, gradientLine } from './layout'
 
 describe('computeLayout · side', () => {
   it('puts the avatar on the left by default', () => {
@@ -139,30 +139,60 @@ describe('gradientLine', () => {
 
 describe('fontString', () => {
   it('omits a normal weight', () => {
-    expect(fontString('normal', 32, 'Noto Sans JP')).toBe('32px Noto Sans JP')
+    expect(fontString('normal', 32, 'Noto Sans JP')).toBe('32px "Noto Sans JP"')
   })
 
   it('includes a keyword weight', () => {
-    expect(fontString('bold', 32, 'Noto Sans JP')).toBe('bold 32px Noto Sans JP')
+    expect(fontString('bold', 32, 'Noto Sans JP')).toBe('bold 32px "Noto Sans JP"')
   })
 
   it('includes a numeric weight', () => {
-    expect(fontString(700, 32, 'Noto Sans JP')).toBe('700 32px Noto Sans JP')
+    expect(fontString(700, 32, 'Noto Sans JP')).toBe('700 32px "Noto Sans JP"')
   })
 
   it('omits italic by default', () => {
-    expect(fontString('normal', 32, 'Noto Sans JP')).toBe('32px Noto Sans JP')
+    expect(fontString('normal', 32, 'Noto Sans JP')).toBe('32px "Noto Sans JP"')
   })
 
   it('prefixes italic before the weight, in CSS shorthand order', () => {
-    expect(fontString('bold', 32, 'Noto Sans JP', true)).toBe('italic bold 32px Noto Sans JP')
+    expect(fontString('bold', 32, 'Noto Sans JP', true)).toBe('italic bold 32px "Noto Sans JP"')
   })
 
   it('prefixes italic even with a normal weight', () => {
-    expect(fontString('normal', 32, 'Noto Sans JP', true)).toBe('italic 32px Noto Sans JP')
+    expect(fontString('normal', 32, 'Noto Sans JP', true)).toBe('italic 32px "Noto Sans JP"')
   })
 
   it('prefixes italic before a numeric weight', () => {
-    expect(fontString(700, 32, 'Noto Sans JP', true)).toBe('italic 700 32px Noto Sans JP')
+    expect(fontString(700, 32, 'Noto Sans JP', true)).toBe('italic 700 32px "Noto Sans JP"')
+  })
+
+  it('quotes every family in a stack', () => {
+    expect(fontString('normal', 32, 'M PLUS Rounded 1c, Noto Sans JP, sans-serif')).toBe(
+      '32px "M PLUS Rounded 1c", "Noto Sans JP", sans-serif',
+    )
+  })
+})
+
+describe('cssFontFamily', () => {
+  it('quotes a family that is not a valid CSS identifier', () => {
+    expect(cssFontFamily('M PLUS Rounded 1c')).toBe('"M PLUS Rounded 1c"')
+  })
+
+  it('leaves generic keywords unquoted, in any case', () => {
+    expect(cssFontFamily('serif, Sans-Serif, monospace, system-ui')).toBe(
+      'serif, Sans-Serif, monospace, system-ui',
+    )
+  })
+
+  it('keeps already-quoted families as written, commas included', () => {
+    expect(cssFontFamily(`"Foo, Bar", 'Baz', Qux`)).toBe(`"Foo, Bar", 'Baz', "Qux"`)
+  })
+
+  it('escapes quotes and backslashes inside a family', () => {
+    expect(cssFontFamily('A"B\\C')).toBe('"A\\"B\\\\C"')
+  })
+
+  it('drops empty entries and surrounding whitespace', () => {
+    expect(cssFontFamily(' Noto Sans JP ,, sans-serif ')).toBe('"Noto Sans JP", sans-serif')
   })
 })
diff --git a/src/render/layout.ts b/src/render/layout.ts
index d36c230..beb1ebc 100644
--- a/src/render/layout.ts
+++ b/src/render/layout.ts
@@ -116,6 +116,40 @@ export function watermarkCorner(theme: Theme): 'bottom-right' | 'bottom-left' |
   return theme.avatar.position === 'right' ? 'bottom-left' : 'bottom-right'
 }
 
+/** CSS generic family keywords, which name no real font and so must stay unquoted. */
+const GENERIC_FAMILIES = new Set([
+  'serif',
+  'sans-serif',
+  'monospace',
+  'cursive',
+  'fantasy',
+  'system-ui',
+  'emoji',
+  'math',
+  'fangsong',
+  'ui-serif',
+  'ui-sans-serif',
+  'ui-monospace',
+  'ui-rounded',
+])
+
+/**
+ * Quotes every family in a comma-separated list, leaving generic keywords and already-quoted names alone.
+ *
+ * `@napi-rs/canvas` 1.0.12+ parses `ctx.font` like Blink, which rejects the whole value when an unquoted family is not a valid CSS identifier sequence (the `1c` in `M PLUS Rounded 1c`) and silently keeps the previous font instead.
+ */
+export function cssFontFamily(families: string): string {
+  return (families.match(/"[^"]*"|'[^']*'|[^,]+/g) ?? [])
+    .map((family) => family.trim())
+    .filter((family) => family !== '')
+    .map((family) =>
+      /^["']/.test(family) || GENERIC_FAMILIES.has(family.toLowerCase())
+        ? family
+        : `"${family.replace(/["\\]/g, '\\$&')}"`,
+    )
+    .join(', ')
+}
+
 /**
  * Builds the CSS font shorthand a canvas context expects.
  *
@@ -129,7 +163,7 @@ export function fontString(
 ): string {
   const stylePrefix = italic ? 'italic ' : ''
   const weightPart = weight === 'normal' ? '' : `${weight} `
-  return `${stylePrefix}${weightPart}${size}px ${family}`
+  return `${stylePrefix}${weightPart}${size}px ${cssFontFamily(family)}`
 }
 
 /** Resolves a size that may be a fraction of the canvas height, or pixels. */
diff --git a/src/render/textStyle.ts b/src/render/textStyle.ts
index 9353ace..c47c5ac 100644
--- a/src/render/textStyle.ts
+++ b/src/render/textStyle.ts
@@ -1,5 +1,6 @@
 import type { FontWeight } from '../theme/types'
 import type { SKRSContext2D } from './canvasFactory'
+import { fontString } from './layout'
 
 /** Mixed script, so the probe catches fonts that only vary in one of them. */
 const PROBE = 'AWMil あ漢'
@@ -32,9 +33,9 @@ function detect(ctx: SKRSContext2D, family: string): boolean {
   if (cached !== undefined) return cached
 
   const previous = ctx.font
-  ctx.font = `100px ${family}`
+  ctx.font = fontString('normal', 100, family)
   const regular = ctx.measureText(PROBE).width
-  ctx.font = `bold 100px ${family}`
+  ctx.font = fontString('bold', 100, family)
   const bold = ctx.measureText(PROBE).width
   ctx.font = previous