diff --git a/persistent-data/run_set.h b/persistent-data/run_set.h
index a061487..b3098d6 100644
--- a/persistent-data/run_set.h
+++ b/persistent-data/run_set.h
@@ -99,6 +99,8 @@ namespace base {
 				replacement.insert(run<T>());
 			else {
 				typename rset::const_iterator b = runs_.begin();
+
+				// Some versions of gcc give a spurious warning here.
 				maybe last = b->end_;
 
 				if (b->begin_)