diff --git a/apps/web/src/themePalette.test.ts b/apps/web/src/themePalette.test.ts
index 55f73552e339e..1364e57409336 100644
--- a/apps/web/src/themePalette.test.ts
+++ b/apps/web/src/themePalette.test.ts
@@ -63,6 +63,17 @@ function contrastRatio(first: string, second: string): number {
 }
 
 describe("theme files", () => {
+  it("gives non-Latin theme names distinct stable ids", () => {
+    const file = {
+      version: THEME_FILE_VERSION,
+      appearance: "dark",
+      colors: { canvas: "#101820" },
+    };
+    const night = parseThemeFile({ ...file, name: "夜" });
+    expect(parseThemeFile({ ...file, name: "朝" }).id).not.toBe(night.id);
+    expect(parseThemeFile({ ...file, name: " 夜 " }).id).toBe(night.id);
+  });
+
   it("keeps built-in and standard search pairs readable and distinct from inline code", () => {
     const toOklab = converter("oklab");
     const distance = (first: string, second: string) => {
diff --git a/apps/web/src/themePalette.ts b/apps/web/src/themePalette.ts
index 1e9cc1a14d12e..861b415dfa331 100644
--- a/apps/web/src/themePalette.ts
+++ b/apps/web/src/themePalette.ts
@@ -1057,13 +1057,20 @@ export function getThemePreferenceMode(theme: ThemePreference): ThemeAppearance
 }
 
 export function themeIdFromName(name: string): string {
-  const normalized = name
-    .trim()
-    .toLowerCase()
+  const label = name.trim().toLowerCase();
+  const normalized = label
     .replace(/[^a-z0-9]+/g, "-")
     .replace(/^-+|-+$/g, "")
     .slice(0, 48);
-  return normalized || "custom-theme";
+  if (normalized || !label) return normalized || "custom-theme";
+
+  // Names without ASCII letters or digits still need independent, stable ids.
+  let hash = 2_166_136_261;
+  for (let index = 0; index < label.length; index += 1) {
+    hash ^= label.charCodeAt(index);
+    hash = Math.imul(hash, 16_777_619);
+  }
+  return `theme-${(hash >>> 0).toString(36)}`;
 }
 
 export class ThemeLibraryStorageError extends Schema.TaggedError<ThemeLibraryStorageError>()(