diff --git a/src/strconv/itoa_test.go b/src/strconv/itoa_test.go
index e0213ae9af..48dc03e839 100644
--- a/src/strconv/itoa_test.go
+++ b/src/strconv/itoa_test.go
@@ -51,6 +51,7 @@ var itob64tests = []itob64Test{
 	{-0x123456789abcdef, 16, "-123456789abcdef"},
 	{1<<63 - 1, 16, "7fffffffffffffff"},
 	{1<<63 - 1, 2, "111111111111111111111111111111111111111111111111111111111111111"},
+	{-1 << 63, 2, "-1000000000000000000000000000000000000000000000000000000000000000"},
 
 	{16, 17, "g"},
 	{25, 25, "10"},