--- a/security/certverifier/NSSCertDBTrustDomain.cpp
+++ b/security/certverifier/NSSCertDBTrustDomain.cpp
@@ -5,16 +5,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "NSSCertDBTrustDomain.h"
 
 #include <stdint.h>
 
 #include "ExtendedValidation.h"
 #include "OCSPRequestor.h"
+#include "OCSPVerificationTrustDomain.h"
 #include "certdb.h"
 #include "cert.h"
 #include "mozilla/UniquePtr.h"
 #include "nsNSSCertificate.h"
 #include "nss.h"
 #include "NSSErrorsService.h"
 #include "nsServiceManagerUtils.h"
 #include "pk11pub.h"
@@ -633,17 +634,27 @@ NSSCertDBTrustDomain::CheckRevocation(En
 Result
 NSSCertDBTrustDomain::VerifyAndMaybeCacheEncodedOCSPResponse(
   const CertID& certID, Time time, uint16_t maxLifetimeInDays,
   Input encodedResponse, EncodedResponseSource responseSource,
   /*out*/ bool& expired)
 {
   Time thisUpdate(Time::uninitialized);
   Time validThrough(Time::uninitialized);
-  Result rv = VerifyEncodedOCSPResponse(*this, certID, time,
+
+  // We use a try and fallback approach which first mandates good signature
+  // digest algorithms, then falls back to SHA-1 if this fails. If a delegated
+  // OCSP response signing certificate was issued with a SHA-1 signature,
+  // verification initially fails. We cache the failure and then re-use that
+  // result even when doing fallback (i.e. when weak signature digest algorithms
+  // should succeed). To address this we use an OCSPVerificationTrustDomain
+  // here, rather than using *this, to ensure verification succeeds for all
+  // allowed signature digest algorithms.
+  OCSPVerificationTrustDomain trustDomain(*this);
+  Result rv = VerifyEncodedOCSPResponse(trustDomain, certID, time,
                                         maxLifetimeInDays, encodedResponse,
                                         expired, &thisUpdate, &validThrough);
   // If a response was stapled and expired, we don't want to cache it. Return
   // early to simplify the logic here.
   if (responseSource == ResponseWasStapled && expired) {
     PR_ASSERT(rv != Success);
     return rv;
   }

new file mode 100644
--- /dev/null
+++ b/security/certverifier/OCSPVerificationTrustDomain.cpp
@@ -0,0 +1,110 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "OCSPVerificationTrustDomain.h"
+
+using namespace mozilla;
+using namespace mozilla::pkix;
+
+OCSPVerificationTrustDomain::OCSPVerificationTrustDomain(
+  NSSCertDBTrustDomain& certDBTrustDomain)
+  : mCertDBTrustDomain(certDBTrustDomain)
+{
+}
+
+Result
+OCSPVerificationTrustDomain::GetCertTrust(EndEntityOrCA endEntityOrCA,
+                                          const CertPolicyId& policy,
+                                          Input candidateCertDER,
+                                  /*out*/ TrustLevel& trustLevel)
+{
+  return mCertDBTrustDomain.GetCertTrust(endEntityOrCA, policy,
+                                         candidateCertDER, trustLevel);
+}
+
+
+Result
+OCSPVerificationTrustDomain::FindIssuer(Input, IssuerChecker&, Time)
+{
+  // We do not expect this to be called for OCSP signers
+  return Result::FATAL_ERROR_LIBRARY_FAILURE;
+}
+
+Result
+OCSPVerificationTrustDomain::IsChainValid(const DERArray&, Time)
+{
+  // We do not expect this to be called for OCSP signers
+  return Result::FATAL_ERROR_LIBRARY_FAILURE;
+}
+
+Result
+OCSPVerificationTrustDomain::CheckRevocation(EndEntityOrCA, const CertID&,
+                                             Time, Duration, const Input*,
+                                             const Input*)
+{
+  // We do not expect this to be called for OCSP signers
+  return Result::FATAL_ERROR_LIBRARY_FAILURE;
+}
+
+Result
+OCSPVerificationTrustDomain::CheckSignatureDigestAlgorithm(
+  DigestAlgorithm aAlg, EndEntityOrCA aEEOrCA)
+{
+  // The reason for wrapping the NSSCertDBTrustDomain in an
+  // OCSPVerificationTrustDomain is to allow us to bypass the weaker signature
+  // algorithm check - thus all allowable signature digest algorithms should
+  // always be accepted. This is only needed while we gather telemetry on SHA-1.
+  return Success;
+}
+
+Result
+OCSPVerificationTrustDomain::CheckRSAPublicKeyModulusSizeInBits(
+  EndEntityOrCA aEEOrCA, unsigned int aModulusSizeInBits)
+{
+  return mCertDBTrustDomain.
+      CheckRSAPublicKeyModulusSizeInBits(aEEOrCA, aModulusSizeInBits);
+}
+
+Result
+OCSPVerificationTrustDomain::VerifyRSAPKCS1SignedDigest(
+  const SignedDigest& aSignedDigest, Input aSubjectPublicKeyInfo)
+{
+  return mCertDBTrustDomain.VerifyRSAPKCS1SignedDigest(aSignedDigest,
+                                                       aSubjectPublicKeyInfo);
+}
+
+Result
+OCSPVerificationTrustDomain::CheckECDSACurveIsAcceptable(
+  EndEntityOrCA aEEOrCA, NamedCurve aCurve)
+{
+  return mCertDBTrustDomain.CheckECDSACurveIsAcceptable(aEEOrCA, aCurve);
+}
+
+Result
+OCSPVerificationTrustDomain::VerifyECDSASignedDigest(
+  const SignedDigest& aSignedDigest, Input aSubjectPublicKeyInfo)
+{
+  return mCertDBTrustDomain.VerifyECDSASignedDigest(aSignedDigest,
+                                                    aSubjectPublicKeyInfo);
+}
+
+Result
+OCSPVerificationTrustDomain::CheckValidityIsAcceptable(
+  Time notBefore, Time notAfter, EndEntityOrCA endEntityOrCA,
+  KeyPurposeId keyPurpose)
+{
+  return mCertDBTrustDomain.CheckValidityIsAcceptable(notBefore, notAfter,
+                                                      endEntityOrCA,
+                                                      keyPurpose);
+}
+
+Result
+OCSPVerificationTrustDomain::DigestBuf(
+  Input item, DigestAlgorithm digestAlg,
+  /*out*/ uint8_t* digestBuf, size_t digestBufLen)
+{
+  return mCertDBTrustDomain.DigestBuf(item, digestAlg, digestBuf, digestBufLen);
+}

new file mode 100644
--- /dev/null
+++ b/security/certverifier/OCSPVerificationTrustDomain.h
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_psm__OCSPVerificationTrustDomain_h
+#define mozilla_psm__OCSPVerificationTrustDomain_h
+
+#include "pkix/pkixtypes.h"
+#include "NSSCertDBTrustDomain.h"
+
+namespace mozilla { namespace psm {
+
+class OCSPVerificationTrustDomain : public mozilla::pkix::TrustDomain
+{
+public:
+  OCSPVerificationTrustDomain(NSSCertDBTrustDomain& certDBTrustDomain);
+
+  virtual Result FindIssuer(mozilla::pkix::Input encodedIssuerName,
+                            IssuerChecker& checker,
+                            mozilla::pkix::Time time) override;
+
+  virtual Result GetCertTrust(mozilla::pkix::EndEntityOrCA endEntityOrCA,
+                              const mozilla::pkix::CertPolicyId& policy,
+                              mozilla::pkix::Input candidateCertDER,
+                      /*out*/ mozilla::pkix::TrustLevel& trustLevel)
+                              override;
+
+  virtual Result CheckSignatureDigestAlgorithm(
+                   mozilla::pkix::DigestAlgorithm digestAlg,
+                   mozilla::pkix::EndEntityOrCA endEntityOrCA) override;
+
+  virtual Result CheckRSAPublicKeyModulusSizeInBits(
+                   mozilla::pkix::EndEntityOrCA endEntityOrCA,
+                   unsigned int modulusSizeInBits) override;
+
+  virtual Result VerifyRSAPKCS1SignedDigest(
+                   const mozilla::pkix::SignedDigest& signedDigest,
+                   mozilla::pkix::Input subjectPublicKeyInfo) override;
+
+  virtual Result CheckECDSACurveIsAcceptable(
+                   mozilla::pkix::EndEntityOrCA endEntityOrCA,
+                   mozilla::pkix::NamedCurve curve) override;
+
+  virtual Result VerifyECDSASignedDigest(
+                   const mozilla::pkix::SignedDigest& signedDigest,
+                   mozilla::pkix::Input subjectPublicKeyInfo) override;
+
+  virtual Result DigestBuf(mozilla::pkix::Input item,
+                           mozilla::pkix::DigestAlgorithm digestAlg,
+                   /*out*/ uint8_t* digestBuf,
+                           size_t digestBufLen) override;
+
+  virtual Result CheckValidityIsAcceptable(
+                   mozilla::pkix::Time notBefore, mozilla::pkix::Time notAfter,
+                   mozilla::pkix::EndEntityOrCA endEntityOrCA,
+                   mozilla::pkix::KeyPurposeId keyPurpose) override;
+
+  virtual Result CheckRevocation(
+                   mozilla::pkix::EndEntityOrCA endEntityOrCA,
+                   const mozilla::pkix::CertID& certID,
+                   mozilla::pkix::Time time,
+                   mozilla::pkix::Duration validityDuration,
+      /*optional*/ const mozilla::pkix::Input* stapledOCSPResponse,
+      /*optional*/ const mozilla::pkix::Input* aiaExtension)
+                   override;
+
+  virtual Result IsChainValid(const mozilla::pkix::DERArray& certChain,
+                              mozilla::pkix::Time time) override;
+
+private:
+  NSSCertDBTrustDomain& mCertDBTrustDomain;
+};
+
+
+} } // namespace mozilla::psm
+
+#endif // mozilla_psm__OCSPVerificationTrustDomain_h

--- a/security/certverifier/moz.build
+++ b/security/certverifier/moz.build
@@ -9,16 +9,17 @@ EXPORTS += [
     'OCSPCache.h',
 ]
 
 UNIFIED_SOURCES += [
     'CertVerifier.cpp',
     'NSSCertDBTrustDomain.cpp',
     'OCSPCache.cpp',
     'OCSPRequestor.cpp',
+    'OCSPVerificationTrustDomain.cpp',
 ]
 
 if not CONFIG['NSS_NO_EV_CERTS']:
     UNIFIED_SOURCES += [
         'ExtendedValidation.cpp',
     ]
 
 LOCAL_INCLUDES += [