diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 7b4b046764..c78005c9af 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -286,15 +286,9 @@ retry:
 			// swept spans are at the end of the list
 			mSpanList_InsertBack(list, s)
 			unlock(&h.lock)
+			snpages := s.npages
 			if mSpan_Sweep(s, false) {
-				// TODO(rsc,dvyukov): This is probably wrong.
-				// It is undercounting the number of pages reclaimed.
-				// See golang.org/issue/9048.
-				// Note that if we want to add the true count of s's pages,
-				// we must record that before calling mSpan_Sweep,
-				// because if mSpan_Sweep returns true the span has
-				// been
-				n++
+				n += snpages
 			}
 			lock(&h.lock)
 			if n >= npages {