diff --git a/lib/storage/errors.ts b/lib/storage/errors.ts
index 631b01535..1a03b4eeb 100644
--- a/lib/storage/errors.ts
+++ b/lib/storage/errors.ts
@@ -28,15 +28,37 @@ const StorageErrorClass = {
     UNKNOWN: 'unknown',
 } as const;
 
+/**
+ * Serializes non-Error thrown values for classifier matching. JSON.stringify is preferred for plain
+ * objects, but it throws on circular structures and returns undefined for BigInt/function/symbol, so
+ * fall back to String() to keep normalization from throwing before classifyError runs.
+ */
+function serializeThrownValue(error: unknown): string {
+    try {
+        return JSON.stringify(error) ?? String(error);
+    } catch {
+        return String(error);
+    }
+}
+
 /**
  * Normalizes any thrown value into a lowercased `{name, message}` pair for matching. Shared by every
  * provider's classifier so they all extract the error the same way.
  */
 function getErrorParts(error: unknown): {name: string; message: string} {
     if (error instanceof Error || (typeof DOMException !== 'undefined' && error instanceof DOMException)) {
-        return {name: (error.name ?? '').toLowerCase(), message: (error.message ?? '').toLowerCase()};
+        return {
+            name: (error.name ?? '').toLowerCase(),
+            message: (error.message ?? '').toLowerCase(),
+        };
+    }
+    if (typeof error === 'string') {
+        return {name: '', message: error.toLowerCase()};
+    }
+    if (error === null || error === undefined) {
+        return {name: '', message: ''};
     }
-    return {name: '', message: String(error ?? '').toLowerCase()};
+    return {name: '', message: serializeThrownValue(error).toLowerCase()};
 }
 
 export {StorageErrorClass, getErrorParts};
diff --git a/tests/unit/storage/getErrorPartsTest.ts b/tests/unit/storage/getErrorPartsTest.ts
new file mode 100644
index 000000000..54fb7a64f
--- /dev/null
+++ b/tests/unit/storage/getErrorPartsTest.ts
@@ -0,0 +1,40 @@
+import {getErrorParts} from '../../../lib/storage/errors';
+
+describe('getErrorParts', () => {
+    it('should extract name and message from Error instances', () => {
+        expect(getErrorParts(new TypeError('Could not be cloned'))).toEqual({
+            name: 'typeerror',
+            message: 'could not be cloned',
+        });
+    });
+
+    it('should lowercase string throws', () => {
+        expect(getErrorParts('Quota exceeded')).toEqual({name: '', message: 'quota exceeded'});
+    });
+
+    it('should treat null and undefined as empty', () => {
+        expect(getErrorParts(null)).toEqual({name: '', message: ''});
+        expect(getErrorParts(undefined)).toEqual({name: '', message: ''});
+    });
+
+    it('should serialize plain objects so classifiers can match fields', () => {
+        expect(getErrorParts({message: 'QuotaExceededError'})).toEqual({
+            name: '',
+            message: '{"message":"quotaexceedederror"}',
+        });
+    });
+
+    it('should not throw on circular objects', () => {
+        const circular: {self?: unknown} = {};
+        circular.self = circular;
+
+        expect(() => getErrorParts(circular)).not.toThrow();
+        expect(getErrorParts(circular)).toEqual({name: '', message: '[object object]'});
+    });
+
+    it('should not throw on BigInt', () => {
+        const value = BigInt(1);
+        expect(() => getErrorParts(value)).not.toThrow();
+        expect(getErrorParts(value)).toEqual({name: '', message: '1'});
+    });
+});