diff --git a/src/pkg/asn1/marshal.go b/src/pkg/asn1/marshal.go
index d4f8f782d45..328042b2b2c 100644
--- a/src/pkg/asn1/marshal.go
+++ b/src/pkg/asn1/marshal.go
@@ -123,13 +123,20 @@ func marshalInt64(out *forkableWriter, i int64) (err os.Error) {
 }
 
 func int64Length(i int64) (numBytes int) {
-	if i == 0 {
-		return 1
+	numBytes = 1
+
+	if i > 0 {
+		for i > 127 {
+			numBytes++
+			i >>= 8
+		}
 	}
 
-	for i > 0 {
-		numBytes++
-		i >>= 8
+	if i < 0 {
+		for i < -128 {
+			numBytes++
+			i >>= 8
+		}
 	}
 
 	return
diff --git a/src/pkg/asn1/marshal_test.go b/src/pkg/asn1/marshal_test.go
index 67878f9bb93..492f39dace3 100644
--- a/src/pkg/asn1/marshal_test.go
+++ b/src/pkg/asn1/marshal_test.go
@@ -59,6 +59,10 @@ type marshalTest struct {
 
 var marshalTests = []marshalTest{
 	marshalTest{10, "02010a"},
+	marshalTest{127, "02017f"},
+	marshalTest{128, "02020080"},
+	marshalTest{-128, "020180"},
+	marshalTest{-129, "0202ff7f"},
 	marshalTest{intStruct{64}, "3003020140"},
 	marshalTest{twoIntStruct{64, 65}, "3006020140020141"},
 	marshalTest{nestedStruct{intStruct{127}}, "3005300302017f"},