diff --git a/e2e/js_run_devserver/src/BUILD.bazel b/e2e/js_run_devserver/src/BUILD.bazel
index 50cefe249..f26466335 100644
--- a/e2e/js_run_devserver/src/BUILD.bazel
+++ b/e2e/js_run_devserver/src/BUILD.bazel
@@ -121,6 +121,7 @@ js_run_devserver(
         ":web_files",
     ],
     log_level = "debug",
+    grant_sandbox_write_permissions = True,
 )
 
 # Now the js_binary variant
@@ -141,6 +142,7 @@ js_run_devserver(
     ],
     log_level = "debug",
     tool = ":simple_bin",
+    grant_sandbox_write_permissions = True,
 )
 
 # Intentionally a js_library and not a js_binary to test that transitive npm are
diff --git a/js/private/js_run_devserver.mjs b/js/private/js_run_devserver.mjs
index ae9503124..dc35e1b75 100644
--- a/js/private/js_run_devserver.mjs
+++ b/js/private/js_run_devserver.mjs
@@ -214,14 +214,11 @@ async function syncRecursive(src, dst, sandbox, writePerm) {
 
             if (process.env.JS_BINARY__LOG_DEBUG) {
                 console.error(
-                    `Syncing file ${src.slice(
-                        RUNFILES_ROOT.length + 1
-                    )} (${friendlyFileSize(lstat.size)})`
+                    `Syncing file ${src} (${friendlyFileSize(lstat.size)}) to ${dst}`
                 )
+                console.error(`Dst exists: ${exists}`)
             }
-            if (exists) {
-                await fs.promises.unlink(dst)
-            } else {
+            if (!exists) {
                 // Intentionally synchronous; see comment on mkdirpSync
                 mkdirpSync(path.dirname(dst))
             }