diff --git a/libc/private/bionic_lock.h b/libc/private/bionic_lock.h
index eebfeff..410e637 100644
--- a/libc/private/bionic_lock.h
+++ b/libc/private/bionic_lock.h
@@ -78,7 +78,7 @@
 
 class LockGuard {
  public:
-  LockGuard(Lock& lock) : lock_(lock) {
+  explicit LockGuard(Lock& lock) : lock_(lock) {
     lock_.lock();
   }
   ~LockGuard() {