diff --git a/src/browser/WebSourceMapFetcher.ts b/src/browser/WebSourceMapFetcher.ts
index 546fd9d97..3c2d3ae81 100644
--- a/src/browser/WebSourceMapFetcher.ts
+++ b/src/browser/WebSourceMapFetcher.ts
@@ -180,6 +180,15 @@ class SourceMapEncodingError extends Error {
   }
 }
 
+class SourceMapRedirectLocationError extends Error {
+  constructor(url: string, location: string) {
+    super(
+      `Source-map redirect from ${JSON.stringify(url)} supplied an invalid Location URL: ${JSON.stringify(location)}.`,
+    );
+    this.name = "SourceMapRedirectLocationError";
+  }
+}
+
 const fetchOne = async (
   request: WebSourceMapRequest,
   input: AnalyzeWebBundleInput,
@@ -250,11 +259,11 @@ const fetchOne = async (
     return emptySourceMapItem(
       request,
       "fetch_failed",
-      cause instanceof SourceMapSizeLimitError
+      cause instanceof SourceMapRedirectLocationError ||
+        cause instanceof SourceMapSizeLimitError ||
+        cause instanceof SourceMapDeadlineError
         ? cause.message
-        : cause instanceof SourceMapDeadlineError
-          ? cause.message
-          : "Source-map fetch or validation failed.",
+        : "Source-map fetch or validation failed.",
     );
   }
 };
@@ -296,7 +305,11 @@ const fetchFollowingApprovedRedirects = async (
     const location = response.headers.get("location");
     if (location === null) return { response, fetchedUrl: current };
     await response.body?.cancel();
-    current = new URL(location, current).href;
+    try {
+      current = new URL(location, current).href;
+    } catch {
+      throw new SourceMapRedirectLocationError(current, location);
+    }
   }
 };
 
diff --git a/tests/boundary/browser/cdpBrowserProvider.document_script.test.ts b/tests/boundary/browser/cdpBrowserProvider.document_script.test.ts
index 9a859f034..7131b30d8 100644
--- a/tests/boundary/browser/cdpBrowserProvider.document_script.test.ts
+++ b/tests/boundary/browser/cdpBrowserProvider.document_script.test.ts
@@ -143,6 +143,7 @@ describe("CdpBrowserProvider: approved accessibility and source capture", () =>
       items: [
         {
           status: "included",
+          declared_url: `${browser.allowedOrigin}/app.js.map?token=map-secret`,
           original_sources: [
             expect.objectContaining({
               source: `${browser.allowedOrigin}/src/main.ts`,
diff --git a/tests/boundary/browser/webSourceMapHttpStatus.test.ts b/tests/boundary/browser/webSourceMapHttpStatus.test.ts
index 69763ddf9..f07419968 100644
--- a/tests/boundary/browser/webSourceMapHttpStatus.test.ts
+++ b/tests/boundary/browser/webSourceMapHttpStatus.test.ts
@@ -85,3 +85,41 @@ it.each([
     }
   },
 );
+
+it("keeps the declared URL and reports malformed redirect Location evidence", async () => {
+  const declaredUrl = "https://app.example.test/declared.map";
+  const input = analyzeWebBundleInputSchema.parse({
+    cdp_endpoint: "http://127.0.0.1:9222",
+    target_id: "selected-page",
+    allowed_origins: ["https://app.example.test"],
+    fetch_source_maps: true,
+  });
+  const result = await fetchWebSourceMaps(
+    [
+      {
+        scriptKey: `scr_${"1".repeat(64)}`,
+        declaredUrl,
+        fetchUrl: declaredUrl,
+      },
+    ],
+    input,
+    undefined,
+    {
+      fetch: () =>
+        Promise.resolve(
+          new Response(null, {
+            status: 302,
+            headers: { location: "http://[invalid" },
+          }),
+        ),
+    },
+  );
+
+  expect(result.items[0]).toMatchObject({
+    status: "fetch_failed",
+    declared_url: declaredUrl,
+    limitation: expect.stringContaining("invalid Location URL"),
+  });
+  expect(result.items[0]?.limitation).toContain(declaredUrl);
+  expect(result.items[0]?.limitation).toContain("http://[invalid");
+});