diff --git a/source/threads.tex b/source/threads.tex
index 7bab867c50..7925987968 100644
--- a/source/threads.tex
+++ b/source/threads.tex
@@ -7588,7 +7588,7 @@
 
     // \ref{thread.lock.unique.obs}, observers
     bool owns_lock() const noexcept;
-    explicit operator bool () const noexcept;
+    explicit operator bool() const noexcept;
     mutex_type* mutex() const noexcept;
 
   private: