diff --git a/packages/core/src/fs-util.ts b/packages/core/src/fs-util.ts
index 24263cbadf93..293160b9a42d 100644
--- a/packages/core/src/fs-util.ts
+++ b/packages/core/src/fs-util.ts
@@ -54,9 +54,13 @@ export namespace FSUtil {
       })
 
       const readFileStringSafe = Effect.fn("FileSystem.readFileStringSafe")(function* (path: string) {
-        return yield* fs
-          .readFileString(path)
-          .pipe(Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(undefined)))
+        return yield* fs.readFileString(path).pipe(
+          Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(undefined)),
+          // A probed path that turns out to be a directory yields EISDIR, which the
+          // platform layer reports as BadResource. Treat it like a missing file so
+          // callers walking config locations don't crash on a directory match.
+          Effect.catchReason("PlatformError", "BadResource", () => Effect.succeed(undefined)),
+        )
       })
 
       const isDir = Effect.fn("FileSystem.isDir")(function* (path: string) {
diff --git a/packages/core/test/filesystem/filesystem.test.ts b/packages/core/test/filesystem/filesystem.test.ts
index 10f61d8a97f9..7deb25d7e56c 100644
--- a/packages/core/test/filesystem/filesystem.test.ts
+++ b/packages/core/test/filesystem/filesystem.test.ts
@@ -91,6 +91,20 @@ describe("FSUtil", () => {
         expect(result).toBeUndefined()
       }),
     )
+
+    it(
+      "returns undefined when the path is a directory (EISDIR)",
+      Effect.gen(function* () {
+        const fs = yield* FSUtil.Service
+        const filesys = yield* FileSystem.FileSystem
+        const tmp = yield* filesys.makeTempDirectoryScoped()
+        const dir = path.join(tmp, "subdir")
+        yield* filesys.makeDirectory(dir)
+
+        const result = yield* fs.readFileStringSafe(dir)
+        expect(result).toBeUndefined()
+      }),
+    )
   })
 
   describe("readJson / writeJson", () => {