diff --git a/lib/memory.c b/lib/memory.c
index 1137390cb..6c97e190a 100644
--- a/lib/memory.c
+++ b/lib/memory.c
@@ -51,7 +51,10 @@ static void memory_init(void);
 
 /* Runs the memory monitor.
  *
- * The client should call memory_should_report() afterward. */
+ * The client should call memory_should_report() afterward.
+ *
+ * This function, and the remainder of this module's interface, should be
+ * called from only a single thread. */
 void
 memory_run(void)
 {