diff --git a/packages/fuzzer/trace.test.ts b/packages/fuzzer/trace.test.ts
new file mode 100644
index 00000000..c8148c78
--- /dev/null
+++ b/packages/fuzzer/trace.test.ts
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2026 Code Intelligence GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { addon } from "./addon";
+import { tracer } from "./trace";
+
+// Avoid loading the native addon, which is not available in the unit test
+// environment. Only the tracing entry points used below are needed.
+jest.mock("./addon", () => ({
+	addon: {
+		tracePcIndir: jest.fn(),
+		traceUnequalStrings: jest.fn(),
+		traceStringContainment: jest.fn(),
+		traceIntegerCompare: jest.fn(),
+	},
+}));
+
+describe("exploreState", () => {
+	beforeEach(() => {
+		(addon.tracePcIndir as jest.Mock).mockClear();
+	});
+
+	it("forwards a numeric state to the fuzzer", () => {
+		tracer.exploreState(1337, 7);
+		expect(addon.tracePcIndir).toHaveBeenCalledWith(7, 1337);
+	});
+
+	it("ignores non-numeric state", () => {
+		tracer.exploreState("1337" as unknown as number, 7);
+		expect(addon.tracePcIndir).not.toHaveBeenCalled();
+	});
+
+	it("ignores non-numeric id", () => {
+		tracer.exploreState(1337, "7" as unknown as number);
+		expect(addon.tracePcIndir).not.toHaveBeenCalled();
+	});
+});
diff --git a/packages/fuzzer/trace.ts b/packages/fuzzer/trace.ts
index 753f468b..e9c8587b 100644
--- a/packages/fuzzer/trace.ts
+++ b/packages/fuzzer/trace.ts
@@ -212,7 +212,7 @@ function guideTowardsContainment(needle: string, haystack: string, id: number) {
 export function exploreState(state: number, id: number) {
 	// Check types as JavaScript fuzz targets could provide wrong ones.
 	// noinspection SuspiciousTypeOfGuard
-	if (typeof state !== "string" || typeof id !== "number") {
+	if (typeof state !== "number" || typeof id !== "number") {
 		return;
 	}
 	tracer.tracePcIndir(id, state);