diff --git a/tools/release/highlight-cards.mjs b/tools/release/highlight-cards.mjs
index 8ba5a6225..79bed39ec 100644
--- a/tools/release/highlight-cards.mjs
+++ b/tools/release/highlight-cards.mjs
@@ -78,6 +78,53 @@ export function escapeXml(text) {
 const WIDE_GLYPHS = new Set('MWmw@%ЖШЩбюфЮ');
 const NARROW_GLYPHS = new Set("iljItfrJ.,;:'\"`!|()[]{}/\\-ЁІ");
 
+/**
+ * @param {string} text
+ * @param {number} fontSize
+ * @returns {number} estimated rendered width in pixels
+ */
+/**
+ * Latin (through Extended-B), Greek and Cyrillic plus ASCII punctuation — the
+ * scripts the factors above were calibrated on.
+ */
+function isCalibratedScript(codePoint) {
+    return (
+        codePoint <= 0x024f || (codePoint >= 0x0370 && codePoint <= 0x04ff)
+    );
+}
+
+/**
+ * @param {string} character a single code point
+ * @returns {number} advance width as a fraction of the font size
+ */
+function advanceFactor(character) {
+    if (character === ' ') {
+        return 0.3;
+    }
+
+    if (NARROW_GLYPHS.has(character)) {
+        return 0.35;
+    }
+
+    if (WIDE_GLYPHS.has(character)) {
+        return 1.1;
+    }
+
+    // Anything outside the calibrated scripts is assumed full-width. CJK,
+    // kana, hangul and emoji genuinely are around one em, and for a narrow
+    // script the cost of guessing wide is an early line break — invisible —
+    // against a cropped card for guessing narrow.
+    if (!isCalibratedScript(character.codePointAt(0))) {
+        return 1.1;
+    }
+
+    const isUppercase =
+        character === character.toUpperCase() &&
+        character !== character.toLowerCase();
+
+    return isUppercase ? 0.78 : 0.6;
+}
+
 /**
  * @param {string} text
  * @param {number} fontSize
@@ -86,18 +133,9 @@ const NARROW_GLYPHS = new Set("iljItfrJ.,;:'\"`!|()[]{}/\\-ЁІ");
 export function estimateTextWidth(text, fontSize) {
     let units = 0;
 
+    // Iterating the string yields code points, so an emoji counts once.
     for (const character of text) {
-        if (character === ' ') {
-            units += 0.3;
-        } else if (NARROW_GLYPHS.has(character)) {
-            units += 0.35;
-        } else if (WIDE_GLYPHS.has(character)) {
-            units += 1.1;
-        } else if (character === character.toUpperCase() && character !== character.toLowerCase()) {
-            units += 0.78;
-        } else {
-            units += 0.6;
-        }
+        units += advanceFactor(character);
     }
 
     return units * fontSize;
diff --git a/tools/release/highlight-cards.test.mjs b/tools/release/highlight-cards.test.mjs
index 390323fd2..273796659 100644
--- a/tools/release/highlight-cards.test.mjs
+++ b/tools/release/highlight-cards.test.mjs
@@ -125,6 +125,25 @@ describe('wrapText', () => {
         }
     });
 
+    it('treats uncalibrated scripts as full-width rather than narrow', () => {
+        // CJK, kana, hangul and emoji are ~1 em; falling through to the
+        // lowercase-Latin factor let a 60-glyph headline paint off-canvas.
+        for (const glyph of ['界', 'ひ', '한', '🎉', 'Ω'.repeat(1)]) {
+            const wide = estimateTextWidth(glyph.repeat(28), 52);
+
+            assert.ok(
+                wide > TEXT_MAX_WIDTH,
+                `28 × "${glyph}" estimates only ${Math.round(wide)}px`
+            );
+        }
+    });
+
+    it('keeps a full-width headline inside the canvas', () => {
+        for (const line of wrapText('界'.repeat(60), budget(TEXT_MAX_WIDTH, 52, 2))) {
+            assert.ok(estimateTextWidth(line, 52) <= TEXT_MAX_WIDTH, line);
+        }
+    });
+
     it('estimates a wide glyph run near its measured rendered width', () => {
         // Calibration anchor: 34 `W` at font-size 52 renders ~1948px.
         const estimate = estimateTextWidth('W'.repeat(34), 52);