--- a/security/sandbox/linux/SandboxInfo.cpp
+++ b/security/sandbox/linux/SandboxInfo.cpp
@@ -132,31 +132,16 @@ CanCreateUserNamespace()
   // This is run at static initializer time, while single-threaded, so
   // locking isn't needed to access the environment.
   static const char kCacheEnvName[] = "MOZ_ASSUME_USER_NS";
   const char* cached = getenv(kCacheEnvName);
   if (cached) {
     return cached[0] > '0';
   }
 
-  // Valgrind might allow the clone, but doesn't know what to do with
-  // unshare.  Check for that by unsharing nothing.  (Valgrind will
-  // probably need sandboxing disabled entirely, but no need to break
-  // things worse than strictly necessary.)
-  if (syscall(__NR_unshare, 0) != 0) {
-#ifdef MOZ_VALGRIND
-    MOZ_ASSERT(errno == ENOSYS);
-#else
-    // If something else can cause that call to fail, we's like to know
-    // about it; the right way to handle it might not be the same.
-    MOZ_ASSERT(false);
-#endif
-    return false;
-  }
-
   pid_t pid = syscall(__NR_clone, SIGCHLD | CLONE_NEWUSER,
                       nullptr, nullptr, nullptr, nullptr);
   if (pid == 0) {
     // In the child.  Do as little as possible.
     _exit(0);
   }
   if (pid == -1) {
     // Failure.