diff --git a/etcdserver/api/v3rpc/rpctypes/error.go b/etcdserver/api/v3rpc/rpctypes/error.go
index e6a281460..26e3fd378 100644
--- a/etcdserver/api/v3rpc/rpctypes/error.go
+++ b/etcdserver/api/v3rpc/rpctypes/error.go
@@ -76,6 +76,12 @@ var (
 	ErrGPRCNotSupportedForLearner     = status.New(codes.Unavailable, "etcdserver: rpc not supported for learner").Err()
 	ErrGRPCBadLeaderTransferee        = status.New(codes.FailedPrecondition, "etcdserver: bad leader transferee").Err()
 
+	ErrGRPCClusterVersionUnavailable     = status.New(codes.Unavailable, "etcdserver: cluster version not found during downgrade").Err()
+	ErrGRPCWrongDowngradeVersionFormat   = status.New(codes.InvalidArgument, "etcdserver: wrong downgrade target version format").Err()
+	ErrGRPCInvalidDowngradeTargetVersion = status.New(codes.InvalidArgument, "etcdserver: invalid downgrade target version").Err()
+	ErrGRPCDowngradeInProcess            = status.New(codes.FailedPrecondition, "etcdserver: cluster has a downgrade job in progress").Err()
+	ErrGRPCNoInflightDowngrade           = status.New(codes.FailedPrecondition, "etcdserver: no inflight downgrade job").Err()
+
 	errStringToError = map[string]error{
 		ErrorDesc(ErrGRPCEmptyKey):      ErrGRPCEmptyKey,
 		ErrorDesc(ErrGRPCKeyNotFound):   ErrGRPCKeyNotFound,
@@ -132,6 +138,12 @@ var (
 		ErrorDesc(ErrGRPCCorrupt):                    ErrGRPCCorrupt,
 		ErrorDesc(ErrGPRCNotSupportedForLearner):     ErrGPRCNotSupportedForLearner,
 		ErrorDesc(ErrGRPCBadLeaderTransferee):        ErrGRPCBadLeaderTransferee,
+
+		ErrorDesc(ErrGRPCClusterVersionUnavailable):     ErrGRPCClusterVersionUnavailable,
+		ErrorDesc(ErrGRPCWrongDowngradeVersionFormat):   ErrGRPCWrongDowngradeVersionFormat,
+		ErrorDesc(ErrGRPCInvalidDowngradeTargetVersion): ErrGRPCInvalidDowngradeTargetVersion,
+		ErrorDesc(ErrGRPCDowngradeInProcess):            ErrGRPCDowngradeInProcess,
+		ErrorDesc(ErrGRPCNoInflightDowngrade):           ErrGRPCNoInflightDowngrade,
 	}
 )
 
@@ -190,6 +202,12 @@ var (
 	ErrUnhealthy                  = Error(ErrGRPCUnhealthy)
 	ErrCorrupt                    = Error(ErrGRPCCorrupt)
 	ErrBadLeaderTransferee        = Error(ErrGRPCBadLeaderTransferee)
+
+	ErrClusterVersionUnavailable     = Error(ErrGRPCClusterVersionUnavailable)
+	ErrWrongDowngradeVersionFormat   = Error(ErrGRPCWrongDowngradeVersionFormat)
+	ErrInvalidDowngradeTargetVersion = Error(ErrGRPCInvalidDowngradeTargetVersion)
+	ErrDowngradeInProcess            = Error(ErrGRPCDowngradeInProcess)
+	ErrNoInflightDowngrade           = Error(ErrGRPCNoInflightDowngrade)
 )
 
 // EtcdError defines gRPC server errors.
diff --git a/etcdserver/api/v3rpc/util.go b/etcdserver/api/v3rpc/util.go
index 6027724b2..2ae37af05 100644
--- a/etcdserver/api/v3rpc/util.go
+++ b/etcdserver/api/v3rpc/util.go
@@ -58,6 +58,12 @@ var toGRPCErrorMap = map[error]error{
 	etcdserver.ErrCorrupt:                    rpctypes.ErrGRPCCorrupt,
 	etcdserver.ErrBadLeaderTransferee:        rpctypes.ErrGRPCBadLeaderTransferee,
 
+	etcdserver.ErrClusterVersionUnavailable:     rpctypes.ErrGRPCClusterVersionUnavailable,
+	etcdserver.ErrWrongDowngradeVersionFormat:   rpctypes.ErrGRPCWrongDowngradeVersionFormat,
+	etcdserver.ErrInvalidDowngradeTargetVersion: rpctypes.ErrGRPCInvalidDowngradeTargetVersion,
+	etcdserver.ErrDowngradeInProcess:            rpctypes.ErrGRPCDowngradeInProcess,
+	etcdserver.ErrNoInflightDowngrade:           rpctypes.ErrGRPCNoInflightDowngrade,
+
 	lease.ErrLeaseNotFound:    rpctypes.ErrGRPCLeaseNotFound,
 	lease.ErrLeaseExists:      rpctypes.ErrGRPCLeaseExist,
 	lease.ErrLeaseTTLTooLarge: rpctypes.ErrGRPCLeaseTTLTooLarge,
diff --git a/etcdserver/errors.go b/etcdserver/errors.go
index d0fe28970..dc2a85fdd 100644
--- a/etcdserver/errors.go
+++ b/etcdserver/errors.go
@@ -20,25 +20,30 @@ import (
 )
 
 var (
-	ErrUnknownMethod              = errors.New("etcdserver: unknown method")
-	ErrStopped                    = errors.New("etcdserver: server stopped")
-	ErrCanceled                   = errors.New("etcdserver: request cancelled")
-	ErrTimeout                    = errors.New("etcdserver: request timed out")
-	ErrTimeoutDueToLeaderFail     = errors.New("etcdserver: request timed out, possibly due to previous leader failure")
-	ErrTimeoutDueToConnectionLost = errors.New("etcdserver: request timed out, possibly due to connection lost")
-	ErrTimeoutLeaderTransfer      = errors.New("etcdserver: request timed out, leader transfer took too long")
-	ErrLeaderChanged              = errors.New("etcdserver: leader changed")
-	ErrNotEnoughStartedMembers    = errors.New("etcdserver: re-configuration failed due to not enough started members")
-	ErrLearnerNotReady            = errors.New("etcdserver: can only promote a learner member which is in sync with leader")
-	ErrNoLeader                   = errors.New("etcdserver: no leader")
-	ErrNotLeader                  = errors.New("etcdserver: not leader")
-	ErrRequestTooLarge            = errors.New("etcdserver: request is too large")
-	ErrNoSpace                    = errors.New("etcdserver: no space")
-	ErrTooManyRequests            = errors.New("etcdserver: too many requests")
-	ErrUnhealthy                  = errors.New("etcdserver: unhealthy cluster")
-	ErrKeyNotFound                = errors.New("etcdserver: key not found")
-	ErrCorrupt                    = errors.New("etcdserver: corrupt cluster")
-	ErrBadLeaderTransferee        = errors.New("etcdserver: bad leader transferee")
+	ErrUnknownMethod                 = errors.New("etcdserver: unknown method")
+	ErrStopped                       = errors.New("etcdserver: server stopped")
+	ErrCanceled                      = errors.New("etcdserver: request cancelled")
+	ErrTimeout                       = errors.New("etcdserver: request timed out")
+	ErrTimeoutDueToLeaderFail        = errors.New("etcdserver: request timed out, possibly due to previous leader failure")
+	ErrTimeoutDueToConnectionLost    = errors.New("etcdserver: request timed out, possibly due to connection lost")
+	ErrTimeoutLeaderTransfer         = errors.New("etcdserver: request timed out, leader transfer took too long")
+	ErrLeaderChanged                 = errors.New("etcdserver: leader changed")
+	ErrNotEnoughStartedMembers       = errors.New("etcdserver: re-configuration failed due to not enough started members")
+	ErrLearnerNotReady               = errors.New("etcdserver: can only promote a learner member which is in sync with leader")
+	ErrNoLeader                      = errors.New("etcdserver: no leader")
+	ErrNotLeader                     = errors.New("etcdserver: not leader")
+	ErrRequestTooLarge               = errors.New("etcdserver: request is too large")
+	ErrNoSpace                       = errors.New("etcdserver: no space")
+	ErrTooManyRequests               = errors.New("etcdserver: too many requests")
+	ErrUnhealthy                     = errors.New("etcdserver: unhealthy cluster")
+	ErrKeyNotFound                   = errors.New("etcdserver: key not found")
+	ErrCorrupt                       = errors.New("etcdserver: corrupt cluster")
+	ErrBadLeaderTransferee           = errors.New("etcdserver: bad leader transferee")
+	ErrClusterVersionUnavailable     = errors.New("etcdserver: cluster version not found during downgrade")
+	ErrWrongDowngradeVersionFormat   = errors.New("etcdserver: wrong downgrade target version format")
+	ErrInvalidDowngradeTargetVersion = errors.New("etcdserver: invalid downgrade target version")
+	ErrDowngradeInProcess            = errors.New("etcdserver: cluster has a downgrade job in progress")
+	ErrNoInflightDowngrade           = errors.New("etcdserver: no inflight downgrade job")
 )
 
 type DiscoveryError struct {