src/runtime/mheap.go | 5 +++++

diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index bf682ec97f93b4e6b3fae4225c62f51ac7037540..893587e5d2243a0a99f8a131853a500c7d9a5d3f 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -503,6 +503,11 @@ 	sp := (*slice)(unsafe.Pointer(&h.spans))
 	sp.array = unsafe.Pointer(spansStart)
 	sp.len = 0
 	sp.cap = int(spansBytes / sys.PtrSize)
+
+	// Map metadata structures. But don't map race detector memory
+	// since we're not actually growing the arena here (and TSAN
+	// gets mad if you map 0 bytes).
+	h.setArenaUsed(h.arena_used, false)
 }
 
 // setArenaUsed extends the usable arena to address arena_used and