diff --git a/src/runtime/testdata/testprog/memprof.go b/src/runtime/testdata/testprog/memprof.go
index a22fee61d7..7c700af852 100644
--- a/src/runtime/testdata/testprog/memprof.go
+++ b/src/runtime/testdata/testprog/memprof.go
@@ -14,6 +14,8 @@ import (
 )
 
 func init() {
+	// Force heap sampling for determinism.
+	runtime.MemProfileRate = 1
 	register("MemProf", MemProf)
 }