diff --git a/gennghttpxfun.py b/gennghttpxfun.py
index 7e391d21..f7e202fc 100755
--- a/gennghttpxfun.py
+++ b/gennghttpxfun.py
@@ -168,6 +168,7 @@ OPTIONS = [
     "no-strip-incoming-x-forwarded-proto",
     "ocsp-startup",
     "no-verify-ocsp",
+    "verify-client-tolerate-expired",
 ]
 
 LOGVARS = [
diff --git a/src/shrpx.cc b/src/shrpx.cc
index 95e1dda2..9dbdedb0 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -2137,6 +2137,11 @@ SSL/TLS:
               Path  to file  that contains  CA certificates  to verify
               client certificate.  The file must be in PEM format.  It
               can contain multiple certificates.
+  --verify-client-tolerate-expired
+              Accept  expired  client  certificate.   Operator  should
+              handle  the expired  client  certificate  by some  means
+              (e.g.,  mruby  script).   Otherwise, this  option  might
+              cause a security risk.
   --client-private-key-file=<PATH>
               Path to  file that contains  client private key  used in
               backend client authentication.
@@ -3406,6 +3411,8 @@ int main(int argc, char **argv) {
         {SHRPX_OPT_NO_STRIP_INCOMING_X_FORWARDED_PROTO.c_str(), no_argument,
          &flag, 158},
         {SHRPX_OPT_SINGLE_PROCESS.c_str(), no_argument, &flag, 159},
+        {SHRPX_OPT_VERIFY_CLIENT_TOLERATE_EXPIRED.c_str(), no_argument, &flag,
+         160},
         {nullptr, 0, nullptr, 0}};
 
     int option_index = 0;
@@ -4167,6 +4174,11 @@ int main(int argc, char **argv) {
         cmdcfgs.emplace_back(SHRPX_OPT_SINGLE_PROCESS,
                              StringRef::from_lit("yes"));
         break;
+      case 160:
+        // --verify-client-tolerate-expired
+        cmdcfgs.emplace_back(SHRPX_OPT_VERIFY_CLIENT_TOLERATE_EXPIRED,
+                             StringRef::from_lit("yes"));
+        break;
       default:
         break;
       }
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 21a7e09d..e7efed2b 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -2173,6 +2173,11 @@ int option_lookup_token(const char *name, size_t namelen) {
     break;
   case 30:
     switch (name[29]) {
+    case 'd':
+      if (util::strieq_l("verify-client-tolerate-expire", name, 29)) {
+        return SHRPX_OPTID_VERIFY_CLIENT_TOLERATE_EXPIRED;
+      }
+      break;
     case 'r':
       if (util::strieq_l("strip-incoming-x-forwarded-fo", name, 29)) {
         return SHRPX_OPTID_STRIP_INCOMING_X_FORWARDED_FOR;
@@ -3554,6 +3559,10 @@ int parse_config(Config *config, int optid, const StringRef &opt,
   case SHRPX_OPTID_NO_VERIFY_OCSP:
     config->tls.ocsp.no_verify = util::strieq_l("yes", optarg);
 
+    return 0;
+  case SHRPX_OPTID_VERIFY_CLIENT_TOLERATE_EXPIRED:
+    config->tls.client_verify.tolerate_expired = util::strieq_l("yes", optarg);
+
     return 0;
   case SHRPX_OPTID_CONF:
     LOG(WARN) << "conf: ignored";
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 96bf8c8e..d631a566 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -343,6 +343,8 @@ constexpr auto SHRPX_OPT_NO_STRIP_INCOMING_X_FORWARDED_PROTO =
     StringRef::from_lit("no-strip-incoming-x-forwarded-proto");
 constexpr auto SHRPX_OPT_OCSP_STARTUP = StringRef::from_lit("ocsp-startup");
 constexpr auto SHRPX_OPT_NO_VERIFY_OCSP = StringRef::from_lit("no-verify-ocsp");
+constexpr auto SHRPX_OPT_VERIFY_CLIENT_TOLERATE_EXPIRED =
+    StringRef::from_lit("verify-client-tolerate-expired");
 
 constexpr size_t SHRPX_OBFUSCATED_NODE_LENGTH = 8;
 
@@ -602,6 +604,8 @@ struct TLSConfig {
     // certificate validation
     StringRef cacert;
     bool enabled;
+    // true if we accept an expired client certificate.
+    bool tolerate_expired;
   } client_verify;
 
   // Client (backend connection) TLS configuration.
@@ -1125,6 +1129,7 @@ enum {
   SHRPX_OPTID_USER,
   SHRPX_OPTID_VERIFY_CLIENT,
   SHRPX_OPTID_VERIFY_CLIENT_CACERT,
+  SHRPX_OPTID_VERIFY_CLIENT_TOLERATE_EXPIRED,
   SHRPX_OPTID_WORKER_FRONTEND_CONNECTIONS,
   SHRPX_OPTID_WORKER_READ_BURST,
   SHRPX_OPTID_WORKER_READ_RATE,
diff --git a/src/shrpx_tls.cc b/src/shrpx_tls.cc
index d0bf6085..32818278 100644
--- a/src/shrpx_tls.cc
+++ b/src/shrpx_tls.cc
@@ -94,6 +94,12 @@ int verify_callback(int preverify_ok, X509_STORE_CTX *ctx) {
   if (!preverify_ok) {
     int err = X509_STORE_CTX_get_error(ctx);
     int depth = X509_STORE_CTX_get_error_depth(ctx);
+    if (err == X509_V_ERR_CERT_HAS_EXPIRED && depth == 0 &&
+        get_config()->tls.client_verify.tolerate_expired) {
+      LOG(INFO) << "The client certificate has expired, but is accepted by "
+                   "configuration";
+      return 1;
+    }
     LOG(ERROR) << "client certificate verify error:num=" << err << ":"
                << X509_verify_cert_error_string(err) << ":depth=" << depth;
   }