diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 9542ad8..2d38606 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -22,10 +22,6 @@ jobs:
       - name: Set up Node.js 22
         uses: actions/setup-node@v3
         with:
-          # Always build using the same Node.js version, to ensure consistent
-          # results from scripts/iu-mappings.js.
-          # This version should be the same as the one used in the
-          # publish-on-tag workflow.
           node-version: 22
       - name: Install dependencies
         run: npm install
diff --git a/.github/workflows/publish-on-tag.yml b/.github/workflows/publish-on-tag.yml
index db47cba..b0bc4b8 100644
--- a/.github/workflows/publish-on-tag.yml
+++ b/.github/workflows/publish-on-tag.yml
@@ -14,9 +14,6 @@ jobs:
       - name: Set up Node.js 22
         uses: actions/setup-node@v3
         with:
-          # Always build using the same Node.js version, to ensure consistent
-          # results from scripts/iu-mappings.js.
-          # This version should be the same as the one used in the main workflow.
           node-version: 22
       - name: Install dependencies
         run: npm install
diff --git a/data/i-bmp-mappings.js b/data/i-bmp-mappings.js
index 408c1c3..6d94991 100644
--- a/data/i-bmp-mappings.js
+++ b/data/i-bmp-mappings.js
@@ -210,6 +210,7 @@ module.exports = new Map([
 	[0x198, 0x199],
 	[0x199, 0x198],
 	[0x19A, 0x23D],
+	[0x19B, 0xA7DC],
 	[0x19C, 0x26F],
 	[0x19D, 0x272],
 	[0x19E, 0x220],
@@ -398,6 +399,7 @@ module.exports = new Map([
 	[0x260, 0x193],
 	[0x261, 0xA7AC],
 	[0x263, 0x194],
+	[0x264, 0xA7CB],
 	[0x265, 0xA78D],
 	[0x266, 0xA7AA],
 	[0x268, 0x197],
@@ -1155,6 +1157,8 @@ module.exports = new Map([
 	[0x1C86, 0x44A],
 	[0x1C87, 0x463],
 	[0x1C88, 0xA64B],
+	[0x1C89, 0x1C8A],
+	[0x1C8A, 0x1C89],
 	[0x1C90, 0x10D0],
 	[0x1C91, 0x10D1],
 	[0x1C92, 0x10D2],
@@ -2174,12 +2178,18 @@ module.exports = new Map([
 	[0xA7C8, 0xA7C7],
 	[0xA7C9, 0xA7CA],
 	[0xA7CA, 0xA7C9],
+	[0xA7CB, 0x264],
+	[0xA7CC, 0xA7CD],
+	[0xA7CD, 0xA7CC],
 	[0xA7D0, 0xA7D1],
 	[0xA7D1, 0xA7D0],
 	[0xA7D6, 0xA7D7],
 	[0xA7D7, 0xA7D6],
 	[0xA7D8, 0xA7D9],
 	[0xA7D9, 0xA7D8],
+	[0xA7DA, 0xA7DB],
+	[0xA7DB, 0xA7DA],
+	[0xA7DC, 0x19B],
 	[0xA7F5, 0xA7F6],
 	[0xA7F6, 0xA7F5],
 	[0xAB53, 0xA7B3],
diff --git a/data/iu-mappings.js b/data/iu-mappings.js
index 7ad42d5..318a05d 100644
--- a/data/iu-mappings.js
+++ b/data/iu-mappings.js
@@ -8,7 +8,6 @@ module.exports = new Map([
 	[0xDF, 0x1E9E],
 	[0xE5, 0x212B],
 	[0x17F, 0x53],
-	[0x19B, 0xA7DC],
 	[0x1C4, 0x1C5],
 	[0x1C5, 0x1C4],
 	[0x1C7, 0x1C8],
@@ -17,7 +16,6 @@ module.exports = new Map([
 	[0x1CB, 0x1CA],
 	[0x1F1, 0x1F2],
 	[0x1F2, 0x1F1],
-	[0x264, 0xA7CB],
 	[0x345, 0x1FBE],
 	[0x390, 0x1FD3],
 	[0x392, 0x3D0],
@@ -66,8 +64,6 @@ module.exports = new Map([
 	[0x1C86, 0x42A],
 	[0x1C87, 0x462],
 	[0x1C88, 0xA64A],
-	[0x1C89, 0x1C8A],
-	[0x1C8A, 0x1C89],
 	[0x1E60, 0x1E9B],
 	[0x1E9B, 0x1E60],
 	[0x1E9E, 0xDF],
@@ -141,12 +137,6 @@ module.exports = new Map([
 		0xE5
 	]],
 	[0xA64A, 0x1C88],
-	[0xA7CB, 0x264],
-	[0xA7CC, 0xA7CD],
-	[0xA7CD, 0xA7CC],
-	[0xA7DA, 0xA7DB],
-	[0xA7DB, 0xA7DA],
-	[0xA7DC, 0x19B],
 	[0xFB05, 0xFB06],
 	[0xFB06, 0xFB05],
 	[0x10400, 0x10428],
diff --git a/package.json b/package.json
index 1736416..1a6f853 100644
--- a/package.json
+++ b/package.json
@@ -60,6 +60,6 @@
 	},
 	"devDependencies": {
 		"jsesc": "^3.0.2",
-		"@unicode/unicode-16.0.0": "^1.6.0"
+		"@unicode/unicode-16.0.0": "^1.6.2"
 	}
 }
diff --git a/scripts/case-mappings.js b/scripts/case-mappings.js
index 7ef559b..3ce239f 100644
--- a/scripts/case-mappings.js
+++ b/scripts/case-mappings.js
@@ -77,6 +77,36 @@ const flattenMapping = (mapping, extendFilter) => {
 	return result;
 };
 
+const simpleUppercaseMapping = require('@unicode/unicode-16.0.0/Simple_Case_Mapping/Uppercase/symbols.js');
+const specialUppercaseMapping = require('@unicode/unicode-16.0.0/Special_Casing/Uppercase/symbols.js');
+
+const characterToUppercase = (character) => {
+	// Note: While the spec requires pulling in the Final_Sigma casing context data
+	// (can be accessed from ./Special_Casing/Uppercase--Final_Sigma/) to do a locale-
+	// insensitive full case conversion, we intentionally skip this data because
+	// Final_Sigma should not be activated when there is only one character in the string
+	return (
+		specialUppercaseMapping.get(character) ??
+		simpleUppercaseMapping.get(character) ??
+		character
+	);
+};
+
+// https://tc39.es/ecma262/#sec-runtime-semantics-canonicalize-ch
+const canonicalize = (codepoint) => {
+	// when HasEitherUnicodeFlag is false and rer.[[IgnoreCase]] is true
+	const character = String.fromCodePoint(codepoint);
+	const u = characterToUppercase(character);
+	if (u.length !== 1) {
+		return codepoint;
+	}
+	const cu = u.codePointAt(0);
+	if (codepoint >= 0x7F && cu < 0x7F) {
+		return codepoint;
+	}
+	return cu;
+}
+
 // From <http://unicode.org/Public/UCD/latest/ucd/CaseFolding.txt>:
 //
 // The status field is:
@@ -161,11 +191,7 @@ for (const [from, to] of oneWayMappings) {
 		extend(filteredMappings, from, to);
 	} else {
 		// https://mths.be/es6#sec-runtime-semantics-canonicalize-abstract-operation
-		if(
-			// TODO: Make this not depend on the engine in which this build script
-			// runs. (If V8 has a bug, then the generated data has the same bug.)
-			!RegExp(String.fromCodePoint(from), 'i').test(String.fromCodePoint(to))
-		) {
+		if (canonicalize(from) !== canonicalize(to)) {
 			extend(filteredMappings, from, to);
 		} else if (from > 0x80 || to > 0x80) {
 			extend(filteredBMPMappings, from, to);
diff --git a/tests/fixtures/modifiers.js b/tests/fixtures/modifiers.js
index 50407cf..7c78479 100644
--- a/tests/fixtures/modifiers.js
+++ b/tests/fixtures/modifiers.js
@@ -156,6 +156,11 @@ const modifiersFixtures = [
 		'matches': ['k', 'K', '\u{212A}', '\u{0131}'],
 		'nonMatches': ['0', ',']
 	},
+	{
+		// Unicode 16
+		'pattern': '(?i:\u1C89)',
+		'expected': '(?:[\\u1C89\\u1C8A])'
+	},
 	// +m
 	{
 		'pattern': '(?m:^[a-z])',