diff --git a/crypto/tlscredsx509.c b/crypto/tlscredsx509.c
index 6cc7b53..dc46bc4 100644
--- a/crypto/tlscredsx509.c
+++ b/crypto/tlscredsx509.c
@@ -26,6 +26,516 @@
 
 #ifdef CONFIG_GNUTLS
 
+#include <gnutls/x509.h>
+
+
+static int
+qcrypto_tls_creds_check_cert_times(gnutls_x509_crt_t cert,
+                                   const char *certFile,
+                                   bool isServer,
+                                   bool isCA,
+                                   Error **errp)
+{
+    time_t now = time(NULL);
+
+    if (now == ((time_t)-1)) {
+        error_setg_errno(errp, errno, "cannot get current time");
+        return -1;
+    }
+
+    if (gnutls_x509_crt_get_expiration_time(cert) < now) {
+        error_setg(errp,
+                   (isCA ?
+                    "The CA certificate %s has expired" :
+                    (isServer ?
+                     "The server certificate %s has expired" :
+                     "The client certificate %s has expired")),
+                   certFile);
+        return -1;
+    }
+
+    if (gnutls_x509_crt_get_activation_time(cert) > now) {
+        error_setg(errp,
+                   (isCA ?
+                    "The CA certificate %s is not yet active" :
+                    (isServer ?
+                     "The server certificate %s is not yet active" :
+                     "The client certificate %s is not yet active")),
+                   certFile);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+#if LIBGNUTLS_VERSION_NUMBER >= 2
+/*
+ * The gnutls_x509_crt_get_basic_constraints function isn't
+ * available in GNUTLS 1.0.x branches. This isn't critical
+ * though, since gnutls_certificate_verify_peers2 will do
+ * pretty much the same check at runtime, so we can just
+ * disable this code
+ */
+static int
+qcrypto_tls_creds_check_cert_basic_constraints(QCryptoTLSCredsX509 *creds,
+                                               gnutls_x509_crt_t cert,
+                                               const char *certFile,
+                                               bool isServer,
+                                               bool isCA,
+                                               Error **errp)
+{
+    int status;
+
+    status = gnutls_x509_crt_get_basic_constraints(cert, NULL, NULL, NULL);
+    trace_qcrypto_tls_creds_x509_check_basic_constraints(
+        creds, certFile, status);
+
+    if (status > 0) { /* It is a CA cert */
+        if (!isCA) {
+            error_setg(errp, isServer ?
+                       "The certificate %s basic constraints show a CA, "
+                       "but we need one for a server" :
+                       "The certificate %s basic constraints show a CA, "
+                       "but we need one for a client",
+                       certFile);
+            return -1;
+        }
+    } else if (status == 0) { /* It is not a CA cert */
+        if (isCA) {
+            error_setg(errp,
+                       "The certificate %s basic constraints do not "
+                       "show a CA",
+                       certFile);
+            return -1;
+        }
+    } else if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
+        /* Missing basicConstraints */
+        if (isCA) {
+            error_setg(errp,
+                       "The certificate %s is missing basic constraints "
+                       "for a CA",
+                       certFile);
+            return -1;
+        }
+    } else { /* General error */
+        error_setg(errp,
+                   "Unable to query certificate %s basic constraints: %s",
+                   certFile, gnutls_strerror(status));
+        return -1;
+    }
+
+    return 0;
+}
+#endif
+
+
+static int
+qcrypto_tls_creds_check_cert_key_usage(QCryptoTLSCredsX509 *creds,
+                                       gnutls_x509_crt_t cert,
+                                       const char *certFile,
+                                       bool isCA,
+                                       Error **errp)
+{
+    int status;
+    unsigned int usage = 0;
+    unsigned int critical = 0;
+
+    status = gnutls_x509_crt_get_key_usage(cert, &usage, &critical);
+    trace_qcrypto_tls_creds_x509_check_key_usage(
+        creds, certFile, status, usage, critical);
+
+    if (status < 0) {
+        if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
+            usage = isCA ? GNUTLS_KEY_KEY_CERT_SIGN :
+                GNUTLS_KEY_DIGITAL_SIGNATURE|GNUTLS_KEY_KEY_ENCIPHERMENT;
+        } else {
+            error_setg(errp,
+                       "Unable to query certificate %s key usage: %s",
+                       certFile, gnutls_strerror(status));
+            return -1;
+        }
+    }
+
+    if (isCA) {
+        if (!(usage & GNUTLS_KEY_KEY_CERT_SIGN)) {
+            if (critical) {
+                error_setg(errp,
+                           "Certificate %s usage does not permit "
+                           "certificate signing", certFile);
+                return -1;
+            }
+        }
+    } else {
+        if (!(usage & GNUTLS_KEY_DIGITAL_SIGNATURE)) {
+            if (critical) {
+                error_setg(errp,
+                           "Certificate %s usage does not permit digital "
+                           "signature", certFile);
+                return -1;
+            }
+        }
+        if (!(usage & GNUTLS_KEY_KEY_ENCIPHERMENT)) {
+            if (critical) {
+                error_setg(errp,
+                           "Certificate %s usage does not permit key "
+                           "encipherment", certFile);
+                return -1;
+            }
+        }
+    }
+
+    return 0;
+}
+
+
+static int
+qcrypto_tls_creds_check_cert_key_purpose(QCryptoTLSCredsX509 *creds,
+                                         gnutls_x509_crt_t cert,
+                                         const char *certFile,
+                                         bool isServer,
+                                         Error **errp)
+{
+    int status;
+    size_t i;
+    unsigned int purposeCritical;
+    unsigned int critical;
+    char *buffer = NULL;
+    size_t size;
+    bool allowClient = false, allowServer = false;
+
+    critical = 0;
+    for (i = 0; ; i++) {
+        size = 0;
+        status = gnutls_x509_crt_get_key_purpose_oid(cert, i, buffer,
+                                                     &size, NULL);
+
+        if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
+
+            /* If there is no data at all, then we must allow
+               client/server to pass */
+            if (i == 0) {
+                allowServer = allowClient = true;
+            }
+            break;
+        }
+        if (status != GNUTLS_E_SHORT_MEMORY_BUFFER) {
+            error_setg(errp,
+                       "Unable to query certificate %s key purpose: %s",
+                       certFile, gnutls_strerror(status));
+            return -1;
+        }
+
+        buffer = g_new0(char, size);
+
+        status = gnutls_x509_crt_get_key_purpose_oid(cert, i, buffer,
+                                                     &size, &purposeCritical);
+
+        if (status < 0) {
+            trace_qcrypto_tls_creds_x509_check_key_purpose(
+                creds, certFile, status, "<none>", purposeCritical);
+            g_free(buffer);
+            error_setg(errp,
+                       "Unable to query certificate %s key purpose: %s",
+                       certFile, gnutls_strerror(status));
+            return -1;
+        }
+        trace_qcrypto_tls_creds_x509_check_key_purpose(
+            creds, certFile, status, buffer, purposeCritical);
+        if (purposeCritical) {
+            critical = true;
+        }
+
+        if (g_str_equal(buffer, GNUTLS_KP_TLS_WWW_SERVER)) {
+            allowServer = true;
+        } else if (g_str_equal(buffer, GNUTLS_KP_TLS_WWW_CLIENT)) {
+            allowClient = true;
+        } else if (g_str_equal(buffer, GNUTLS_KP_ANY)) {
+            allowServer = allowClient = true;
+        }
+
+        g_free(buffer);
+    }
+
+    if (isServer) {
+        if (!allowServer) {
+            if (critical) {
+                error_setg(errp,
+                           "Certificate %s purpose does not allow "
+                           "use with a TLS server", certFile);
+                return -1;
+            }
+        }
+    } else {
+        if (!allowClient) {
+            if (critical) {
+                error_setg(errp,
+                           "Certificate %s purpose does not allow use "
+                           "with a TLS client", certFile);
+                return -1;
+            }
+        }
+    }
+
+    return 0;
+}
+
+
+static int
+qcrypto_tls_creds_check_cert(QCryptoTLSCredsX509 *creds,
+                             gnutls_x509_crt_t cert,
+                             const char *certFile,
+                             bool isServer,
+                             bool isCA,
+                             Error **errp)
+{
+    if (qcrypto_tls_creds_check_cert_times(cert, certFile,
+                                           isServer, isCA,
+                                           errp) < 0) {
+        return -1;
+    }
+
+#if LIBGNUTLS_VERSION_NUMBER >= 2
+    if (qcrypto_tls_creds_check_cert_basic_constraints(creds,
+                                                       cert, certFile,
+                                                       isServer, isCA,
+                                                       errp) < 0) {
+        return -1;
+    }
+#endif
+
+    if (qcrypto_tls_creds_check_cert_key_usage(creds,
+                                               cert, certFile,
+                                               isCA, errp) < 0) {
+        return -1;
+    }
+
+    if (!isCA &&
+        qcrypto_tls_creds_check_cert_key_purpose(creds,
+                                                 cert, certFile,
+                                                 isServer, errp) < 0) {
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
+qcrypto_tls_creds_check_cert_pair(gnutls_x509_crt_t cert,
+                                  const char *certFile,
+                                  gnutls_x509_crt_t *cacerts,
+                                  size_t ncacerts,
+                                  const char *cacertFile,
+                                  bool isServer,
+                                  Error **errp)
+{
+    unsigned int status;
+
+    if (gnutls_x509_crt_list_verify(&cert, 1,
+                                    cacerts, ncacerts,
+                                    NULL, 0,
+                                    0, &status) < 0) {
+        error_setg(errp, isServer ?
+                   "Unable to verify server certificate %s against "
+                   "CA certificate %s" :
+                   "Unable to verify client certificate %s against "
+                   "CA certificate %s",
+                   certFile, cacertFile);
+        return -1;
+    }
+
+    if (status != 0) {
+        const char *reason = "Invalid certificate";
+
+        if (status & GNUTLS_CERT_INVALID) {
+            reason = "The certificate is not trusted";
+        }
+
+        if (status & GNUTLS_CERT_SIGNER_NOT_FOUND) {
+            reason = "The certificate hasn't got a known issuer";
+        }
+
+        if (status & GNUTLS_CERT_REVOKED) {
+            reason = "The certificate has been revoked";
+        }
+
+#ifndef GNUTLS_1_0_COMPAT
+        if (status & GNUTLS_CERT_INSECURE_ALGORITHM) {
+            reason = "The certificate uses an insecure algorithm";
+        }
+#endif
+
+        error_setg(errp,
+                   "Our own certificate %s failed validation against %s: %s",
+                   certFile, cacertFile, reason);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static gnutls_x509_crt_t
+qcrypto_tls_creds_load_cert(QCryptoTLSCredsX509 *creds,
+                            const char *certFile,
+                            bool isServer,
+                            Error **errp)
+{
+    gnutls_datum_t data;
+    gnutls_x509_crt_t cert = NULL;
+    char *buf = NULL;
+    gsize buflen;
+    GError *gerr;
+    int ret = -1;
+
+    trace_qcrypto_tls_creds_x509_load_cert(creds, isServer, certFile);
+
+    if (gnutls_x509_crt_init(&cert) < 0) {
+        error_setg(errp, "Unable to initialize certificate");
+        goto cleanup;
+    }
+
+    if (!g_file_get_contents(certFile, &buf, &buflen, &gerr)) {
+        error_setg(errp, "Cannot load CA cert list %s: %s",
+                   certFile, gerr->message);
+        g_error_free(gerr);
+        goto cleanup;
+    }
+
+    data.data = (unsigned char *)buf;
+    data.size = strlen(buf);
+
+    if (gnutls_x509_crt_import(cert, &data, GNUTLS_X509_FMT_PEM) < 0) {
+        error_setg(errp, isServer ?
+                   "Unable to import server certificate %s" :
+                   "Unable to import client certificate %s",
+                   certFile);
+        goto cleanup;
+    }
+
+    ret = 0;
+
+ cleanup:
+    if (ret != 0) {
+        gnutls_x509_crt_deinit(cert);
+        cert = NULL;
+    }
+    g_free(buf);
+    return cert;
+}
+
+
+static int
+qcrypto_tls_creds_load_ca_cert_list(QCryptoTLSCredsX509 *creds,
+                                    const char *certFile,
+                                    gnutls_x509_crt_t *certs,
+                                    unsigned int certMax,
+                                    size_t *ncerts,
+                                    Error **errp)
+{
+    gnutls_datum_t data;
+    char *buf = NULL;
+    gsize buflen;
+    int ret = -1;
+    GError *gerr = NULL;
+
+    *ncerts = 0;
+    trace_qcrypto_tls_creds_x509_load_cert_list(creds, certFile);
+
+    if (!g_file_get_contents(certFile, &buf, &buflen, &gerr)) {
+        error_setg(errp, "Cannot load CA cert list %s: %s",
+                   certFile, gerr->message);
+        g_error_free(gerr);
+        goto cleanup;
+    }
+
+    data.data = (unsigned char *)buf;
+    data.size = strlen(buf);
+
+    if (gnutls_x509_crt_list_import(certs, &certMax, &data,
+                                    GNUTLS_X509_FMT_PEM, 0) < 0) {
+        error_setg(errp,
+                   "Unable to import CA certificate list %s",
+                   certFile);
+        goto cleanup;
+    }
+    *ncerts = certMax;
+
+    ret = 0;
+
+ cleanup:
+    g_free(buf);
+    return ret;
+}
+
+
+#define MAX_CERTS 16
+static int
+qcrypto_tls_creds_x509_sanity_check(QCryptoTLSCredsX509 *creds,
+                                    bool isServer,
+                                    const char *cacertFile,
+                                    const char *certFile,
+                                    Error **errp)
+{
+    gnutls_x509_crt_t cert = NULL;
+    gnutls_x509_crt_t cacerts[MAX_CERTS];
+    size_t ncacerts = 0;
+    size_t i;
+    int ret = -1;
+
+    memset(cacerts, 0, sizeof(cacerts));
+    if (access(certFile, R_OK) == 0) {
+        cert = qcrypto_tls_creds_load_cert(creds,
+                                           certFile, isServer,
+                                           errp);
+        if (!cert) {
+            goto cleanup;
+        }
+    }
+    if (access(cacertFile, R_OK) == 0) {
+        if (qcrypto_tls_creds_load_ca_cert_list(creds,
+                                                cacertFile, cacerts,
+                                                MAX_CERTS, &ncacerts,
+                                                errp) < 0) {
+            goto cleanup;
+        }
+    }
+
+    if (cert &&
+        qcrypto_tls_creds_check_cert(creds,
+                                     cert, certFile, isServer,
+                                     false, errp) < 0) {
+        goto cleanup;
+    }
+
+    for (i = 0; i < ncacerts; i++) {
+        if (qcrypto_tls_creds_check_cert(creds,
+                                         cacerts[i], cacertFile,
+                                         isServer, true, errp) < 0) {
+            goto cleanup;
+        }
+    }
+
+    if (cert && ncacerts &&
+        qcrypto_tls_creds_check_cert_pair(cert, certFile, cacerts,
+                                          ncacerts, cacertFile,
+                                          isServer, errp) < 0) {
+        goto cleanup;
+    }
+
+    ret = 0;
+
+ cleanup:
+    if (cert) {
+        gnutls_x509_crt_deinit(cert);
+    }
+    for (i = 0; i < ncacerts; i++) {
+        gnutls_x509_crt_deinit(cacerts[i]);
+    }
+    return ret;
+}
+
 
 static int
 qcrypto_tls_creds_x509_load(QCryptoTLSCredsX509 *creds,
@@ -71,6 +581,13 @@
         }
     }
 
+    if (creds->sanityCheck &&
+        qcrypto_tls_creds_x509_sanity_check(creds,
+            creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER,
+            cacert, cert, errp) < 0) {
+        goto cleanup;
+    }
+
     ret = gnutls_certificate_allocate_credentials(&creds->data);
     if (ret < 0) {
         error_setg(errp, "Cannot allocate credentials: '%s'",
@@ -204,6 +721,27 @@
 
 
 static void
+qcrypto_tls_creds_x509_prop_set_sanity(Object *obj,
+                                       bool value,
+                                       Error **errp G_GNUC_UNUSED)
+{
+    QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
+
+    creds->sanityCheck = value;
+}
+
+
+static bool
+qcrypto_tls_creds_x509_prop_get_sanity(Object *obj,
+                                       Error **errp G_GNUC_UNUSED)
+{
+    QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
+
+    return creds->sanityCheck;
+}
+
+
+static void
 qcrypto_tls_creds_x509_complete(UserCreatable *uc, Error **errp)
 {
     object_property_set_bool(OBJECT(uc), true, "loaded", errp);
@@ -213,10 +751,18 @@
 static void
 qcrypto_tls_creds_x509_init(Object *obj)
 {
+    QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
+
+    creds->sanityCheck = true;
+
     object_property_add_bool(obj, "loaded",
                              qcrypto_tls_creds_x509_prop_get_loaded,
                              qcrypto_tls_creds_x509_prop_set_loaded,
                              NULL);
+    object_property_add_bool(obj, "sanity-check",
+                             qcrypto_tls_creds_x509_prop_get_sanity,
+                             qcrypto_tls_creds_x509_prop_set_sanity,
+                             NULL);
 }