src/runtime/mheap.go | 4 +++-

diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index db60f7a872708f957259c0a008806a50dd27d973..8db2fcc2888bdb04df7a5abde072404be8d7c4eb 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -917,7 +917,9 @@ 				// will round them *out* and release
 				// more memory than we want.)
 				start = (start + sys.PhysPageSize - 1) &^ (sys.PhysPageSize - 1)
 				end &^= sys.PhysPageSize - 1
-				if start == end {
+				if end <= start {
+					// start and end don't span a
+					// whole physical page.
 					continue
 				}
 			}