diff --git a/lsquic/context/context.nim b/lsquic/context/context.nim
index fed33f0..62f7f82 100644
--- a/lsquic/context/context.nim
+++ b/lsquic/context/context.nim
@@ -247,21 +247,32 @@ proc alpnSelectProtoCB(
 
 proc verifyCertificate(
     ssl: ptr SSL, out_alert: ptr uint8
-): enum_ssl_verify_result_t {.cdecl.} =
-  let sslCtx = SSL_get_SSL_CTX(ssl)
-
-  let quicCtx = cast[QuicContext](SSL_CTX_get_ex_data(sslCtx, SSL_CTX_ID))
-  if quicCtx.isNil:
-    raiseAssert "could not obtain context"
-
-  let derCertificates = getFullCertChain(ssl)
-
-  let serverName = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name)
-  doAssert quicCtx.tlsConfig.certVerifier.isSome, "no custom validator set"
-  if quicCtx.tlsConfig.certVerifier.get().verify($serverName, derCertificates):
-    return ssl_verify_ok
-  else:
-    out_alert[] = SSL_AD_CERTIFICATE_UNKNOWN
+): enum_ssl_verify_result_t {.cdecl, raises: [].} =
+  try:
+    let sslCtx = SSL_get_SSL_CTX(ssl)
+    if sslCtx.isNil:
+      if not out_alert.isNil:
+        out_alert[] = SSL_AD_INTERNAL_ERROR
+      return ssl_verify_invalid
+
+    let quicCtx = cast[QuicContext](SSL_CTX_get_ex_data(sslCtx, SSL_CTX_ID))
+    if quicCtx.isNil or quicCtx.tlsConfig.certVerifier.isNone:
+      if not out_alert.isNil:
+        out_alert[] = SSL_AD_INTERNAL_ERROR
+      return ssl_verify_invalid
+
+    let derCertificates = getFullCertChain(ssl)
+    let serverName = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name)
+    if quicCtx.tlsConfig.certVerifier.get().verify($serverName, derCertificates):
+      return ssl_verify_ok
+
+    if not out_alert.isNil:
+      out_alert[] = SSL_AD_CERTIFICATE_UNKNOWN
+    return ssl_verify_invalid
+  except Exception as exc:
+    warn "certificate verifier raised", errorMsg = exc.msg
+    if not out_alert.isNil:
+      out_alert[] = SSL_AD_CERTIFICATE_UNKNOWN
     return ssl_verify_invalid
 
 proc setupSSLContext*(quicCtx: QuicContext) =
diff --git a/tests/test_verifier.nim b/tests/test_verifier.nim
index 0b93426..8f8d33f 100644
--- a/tests/test_verifier.nim
+++ b/tests/test_verifier.nim
@@ -33,6 +33,13 @@ proc rejectingCertificateCb(
   discard derCertificates
   false
 
+proc raisingCertificateCb(
+    serverName: string, derCertificates: seq[seq[byte]]
+): bool {.gcsafe.} =
+  discard serverName
+  discard derCertificates
+  raise newException(ValueError, "verifier failed")
+
 proc makeRejectingCertificateCb(
     recorder: RejectVerifierRecorder
 ): certificateVerifierCB =
@@ -92,6 +99,18 @@ suite "certificate verifier":
     expect DialError:
       discard await client.dial(listener.localAddress())
 
+  asyncTest "raising client verifier rejects handshake":
+    let client =
+      makeClientWithVerifier(CustomCertificateVerifier.init(raisingCertificateCb))
+    let server =
+      makeServerWithVerifier(CustomCertificateVerifier.init(acceptingCertificateCb))
+    let listener = server.listen(initTAddress("127.0.0.1:0"))
+    defer:
+      await allFutures(client.stop(), listener.stop())
+
+    expect DialError:
+      discard await client.dial(listener.localAddress())
+
   asyncTest "alpn mismatch rejects handshake":
     let client = makeClientWithVerifier(
       CustomCertificateVerifier.init(acceptingCertificateCb), singleAlpn("client-proto")