diff --git a/cmd/heapview/internal/core/mmapfile.go b/cmd/heapview/internal/core/mmapfile.go
index 9886d357..78445a9c 100644
--- a/cmd/heapview/internal/core/mmapfile.go
+++ b/cmd/heapview/internal/core/mmapfile.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 package core
 
 import (
diff --git a/cmd/heapview/internal/core/mmapfile_other.go b/cmd/heapview/internal/core/mmapfile_other.go
new file mode 100644
index 00000000..181f8420
--- /dev/null
+++ b/cmd/heapview/internal/core/mmapfile_other.go
@@ -0,0 +1,14 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!linux
+
+package core
+
+// TODO(matloob): perhaps use the more portable golang.org/x/exp/mmap
+// instead of the mmap code in mmapfile.go.
+
+type mmapFile struct{}
+
+func (m *mmapFile) Close() error { return nil }