diff --git a/src/crypto/x509/x509.go b/src/crypto/x509/x509.go
index bbc63241c6..126432d875 100644
--- a/src/crypto/x509/x509.go
+++ b/src/crypto/x509/x509.go
@@ -909,10 +909,6 @@ func parseCertificate(in *certificate) (*Certificate, error) {
 		return nil, err
 	}
 
-	if in.TBSCertificate.SerialNumber.Sign() < 0 {
-		return nil, errors.New("x509: negative serial number")
-	}
-
 	out.Version = in.TBSCertificate.Version + 1
 	out.SerialNumber = in.TBSCertificate.SerialNumber
 
diff --git a/src/crypto/x509/x509_test.go b/src/crypto/x509/x509_test.go
index 61b1773745..2c01ec7bf1 100644
--- a/src/crypto/x509/x509_test.go
+++ b/src/crypto/x509/x509_test.go
@@ -343,7 +343,11 @@ func TestCreateSelfSignedCertificate(t *testing.T) {
 	for _, test := range tests {
 		commonName := "test.example.com"
 		template := Certificate{
-			SerialNumber: big.NewInt(1),
+			// SerialNumber is negative to ensure that negative
+			// values are parsed. This is due to the prevalence of
+			// buggy code that produces certificates with negative
+			// serial numbers.
+			SerialNumber: big.NewInt(-1),
 			Subject: pkix.Name{
 				CommonName:   commonName,
 				Organization: []string{"Σ Acme Co"},