diff --git a/src/cmd/pack/pack_test.go b/src/cmd/pack/pack_test.go
index cf6121fcc1149..fbc6a3c698200 100644
--- a/src/cmd/pack/pack_test.go
+++ b/src/cmd/pack/pack_test.go
@@ -257,8 +257,15 @@ func TestLargeDefs(t *testing.T) {
 		}
 	}
 
+	n := 10000
+	if testing.Short() {
+		// Issue 9656: 10,000 is too aggressive for several
+		// builders, with ~120 MB of disk consumed. 1,000 is
+		// still enough to exercise the old bug.
+		n = 1000
+	}
 	printf("package large\n\ntype T struct {\n")
-	for i := 0; i < 10000; i++ {
+	for i := 0; i < n; i++ {
 		printf("f%d int `tag:\"", i)
 		for j := 0; j < 100; j++ {
 			printf("t%d=%d,", j, j)