diff --git a/ChangeLog b/ChangeLog
index d16f254..5f60a16 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-05-19  Jean-Paul Calderone  <exarkun@twistedmatrix.com>
+
+	* OpenSSL/crypto/x509.c, OpenSSL/test/test_crypto.py: Add a new
+          method to the X509 type, get_signature_algorithm, for inspecting
+          the signature algorithm field of the certificate.  Based on a
+          patch from <lp:~okuda>.
+
 2011-05-10  Jean-Paul Calderone  <exarkun@twistedmatrix.com>
 
 	* OpenSSL/crypto/crypto.h: Work around a Windows/OpenSSL 1.0 issue
diff --git a/OpenSSL/crypto/x509.c b/OpenSSL/crypto/x509.c
index a12220b..0754dec 100644
--- a/OpenSSL/crypto/x509.c
+++ b/OpenSSL/crypto/x509.c
@@ -519,6 +519,34 @@
     return Py_None;
 }
 
+
+static char crypto_X509_get_signature_algorithm_doc[] = "\n\
+Retrieve the signature algorithm used in the certificate\n\
+\n\
+@return: A byte string giving the name of the signature algorithm used in\n\
+         the certificate.\n\
+@raise ValueError: If the signature algorithm is undefined.\n\
+";
+
+static PyObject *
+crypto_X509_get_signature_algorithm(crypto_X509Obj *self, PyObject *args) {
+    ASN1_OBJECT *alg;
+    int nid;
+
+    if (!PyArg_ParseTuple(args, ":get_signature_algorithm")) {
+        return NULL;
+    }
+
+    alg = self->x509->cert_info->signature->algorithm;
+    nid = OBJ_obj2nid(alg);
+    if (nid == NID_undef) {
+        PyErr_SetString(PyExc_ValueError, "Undefined signature algorithm");
+        return NULL;
+    }
+    return PyBytes_FromString(OBJ_nid2ln(nid));
+}
+
+
 static char crypto_X509_sign_doc[] = "\n\
 Sign the certificate using the supplied key and digest\n\
 \n\
@@ -757,6 +785,7 @@
     ADD_METHOD(set_notAfter),
     ADD_METHOD(gmtime_adj_notBefore),
     ADD_METHOD(gmtime_adj_notAfter),
+    ADD_METHOD(get_signature_algorithm),
     ADD_METHOD(sign),
     ADD_METHOD(has_expired),
     ADD_METHOD(subject_name_hash),
diff --git a/OpenSSL/test/test_crypto.py b/OpenSSL/test/test_crypto.py
index 496dc59..b109b54 100644
--- a/OpenSSL/test/test_crypto.py
+++ b/OpenSSL/test/test_crypto.py
@@ -1474,12 +1474,54 @@
         """
         cert = load_certificate(FILETYPE_PEM, self.pemData)
         self.assertIn(
-            cert.subject_name_hash(), 
+            cert.subject_name_hash(),
             [3350047874, # OpenSSL 0.9.8, MD5
              3278919224, # OpenSSL 1.0.0, SHA1
              ])
 
 
+    def test_get_signature_algorithm(self):
+        """
+        L{X509Type.get_signature_algorithm} returns a string which means
+        the algorithm used to sign the certificate.
+        """
+        cert = load_certificate(FILETYPE_PEM, self.pemData)
+        self.assertEqual(
+            b("sha1WithRSAEncryption"), cert.get_signature_algorithm())
+
+
+    def test_get_undefined_signature_algorithm(self):
+        """
+        L{X509Type.get_signature_algorithm} raises L{ValueError} if the
+        signature algorithm is undefined or unknown.
+        """
+        # This certificate has been modified to indicate a bogus OID in the
+        # signature algorithm field so that OpenSSL does not recognize it.
+        certPEM = """\
+-----BEGIN CERTIFICATE-----
+MIIC/zCCAmigAwIBAgIBATAGBgJ8BQUAMHsxCzAJBgNVBAYTAlNHMREwDwYDVQQK
+EwhNMkNyeXB0bzEUMBIGA1UECxMLTTJDcnlwdG8gQ0ExJDAiBgNVBAMTG00yQ3J5
+cHRvIENlcnRpZmljYXRlIE1hc3RlcjEdMBsGCSqGSIb3DQEJARYObmdwc0Bwb3N0
+MS5jb20wHhcNMDAwOTEwMDk1MTMwWhcNMDIwOTEwMDk1MTMwWjBTMQswCQYDVQQG
+EwJTRzERMA8GA1UEChMITTJDcnlwdG8xEjAQBgNVBAMTCWxvY2FsaG9zdDEdMBsG
+CSqGSIb3DQEJARYObmdwc0Bwb3N0MS5jb20wXDANBgkqhkiG9w0BAQEFAANLADBI
+AkEArL57d26W9fNXvOhNlZzlPOACmvwOZ5AdNgLzJ1/MfsQQJ7hHVeHmTAjM664V
++fXvwUGJLziCeBo1ysWLRnl8CQIDAQABo4IBBDCCAQAwCQYDVR0TBAIwADAsBglg
+hkgBhvhCAQ0EHxYdT3BlblNTTCBHZW5lcmF0ZWQgQ2VydGlmaWNhdGUwHQYDVR0O
+BBYEFM+EgpK+eyZiwFU1aOPSbczbPSpVMIGlBgNVHSMEgZ0wgZqAFPuHI2nrnDqT
+FeXFvylRT/7tKDgBoX+kfTB7MQswCQYDVQQGEwJTRzERMA8GA1UEChMITTJDcnlw
+dG8xFDASBgNVBAsTC00yQ3J5cHRvIENBMSQwIgYDVQQDExtNMkNyeXB0byBDZXJ0
+aWZpY2F0ZSBNYXN0ZXIxHTAbBgkqhkiG9w0BCQEWDm5ncHNAcG9zdDEuY29tggEA
+MA0GCSqGSIb3DQEBBAUAA4GBADv8KpPo+gfJxN2ERK1Y1l17sz/ZhzoGgm5XCdbx
+jEY7xKfpQngV599k1xhl11IMqizDwu0855agrckg2MCTmOI9DZzDD77tAYb+Dk0O
+PEVk0Mk/V0aIsDE9bolfCi/i/QWZ3N8s5nTWMNyBBBmoSliWCm4jkkRZRD0ejgTN
+tgI5
+-----END CERTIFICATE-----
+"""
+        cert = load_certificate(FILETYPE_PEM, certPEM)
+        self.assertRaises(ValueError, cert.get_signature_algorithm)
+
+
 
 class PKCS12Tests(TestCase):
     """
diff --git a/doc/pyOpenSSL.tex b/doc/pyOpenSSL.tex
index 239133f..fa7638d 100644
--- a/doc/pyOpenSSL.tex
+++ b/doc/pyOpenSSL.tex
@@ -321,6 +321,11 @@
 Return the certificate serial number.
 \end{methoddesc}
 
+\begin{methoddesc}[X509]{get_signature_algorithm}{}
+Return the signature algorithm used in the certificate.  If the algorithm is
+undefined, raise \code{ValueError}.
+\end{methoddesc}
+
 \begin{methoddesc}[X509]{get_subject}{}
 Return an X509Name object representing the subject of the certificate.
 \end{methoddesc}