diff --git a/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.pb.go b/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.pb.go
index f8e3939c8..ba4741afd 100644
--- a/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.pb.go
+++ b/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.pb.go
@@ -748,6 +748,8 @@ type UpdateIndexStatusRequest_Repository struct {
 	Branches []*ZoektRepositoryBranch `protobuf:"bytes,2,rep,name=branches,proto3" json:"branches,omitempty"`
 	// index_time_unix is the unix timestamp for when the index was created.
 	IndexTimeUnix int64 `protobuf:"varint,3,opt,name=index_time_unix,json=indexTimeUnix,proto3" json:"index_time_unix,omitempty"`
+	// last_index_error is non-empty when the most recent index attempt failed.
+	LastIndexError string `protobuf:"bytes,4,opt,name=last_index_error,json=lastIndexError,proto3" json:"last_index_error,omitempty"`
 }
 
 func (x *UpdateIndexStatusRequest_Repository) Reset() {
@@ -803,6 +805,13 @@ func (x *UpdateIndexStatusRequest_Repository) GetIndexTimeUnix() int64 {
 	return 0
 }
 
+func (x *UpdateIndexStatusRequest_Repository) GetLastIndexError() string {
+	if x != nil {
+		return x.LastIndexError
+	}
+	return ""
+}
+
 var File_sourcegraph_zoekt_configuration_v1_configuration_proto protoreflect.FileDescriptor
 
 var file_sourcegraph_zoekt_configuration_v1_configuration_proto_rawDesc = []byte{
diff --git a/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.proto b/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.proto
index ecd611d70..d2786961e 100644
--- a/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.proto
+++ b/cmd/zoekt-sourcegraph-indexserver/grpc/protos/sourcegraph/zoekt/configuration/v1/configuration.proto
@@ -154,6 +154,10 @@ message UpdateIndexStatusRequest {
 
     // index_time_unix is the unix timestamp for when the index was created.
     int64 index_time_unix = 3;
+
+    // last_index_error is non-empty when the most recent index attempt failed.
+    // An empty string means the attempt succeeded.
+    string last_index_error = 4;
   }
 
   repeated Repository repositories = 1;
diff --git a/cmd/zoekt-sourcegraph-indexserver/main.go b/cmd/zoekt-sourcegraph-indexserver/main.go
index ad909916d..bc3d21534 100644
--- a/cmd/zoekt-sourcegraph-indexserver/main.go
+++ b/cmd/zoekt-sourcegraph-indexserver/main.go
@@ -677,6 +677,7 @@ func (s *Server) index(ctx context.Context, args *indexArgs) (state indexState,
 
 	err = gitIndex(ctx, c, args, s.Sourcegraph, s.logger)
 	if err != nil {
+		reportIndexFailureToSourcegraph(args, s.Sourcegraph, err, s.logger)
 		return indexStateFail, err
 	}
 
@@ -692,6 +693,25 @@ func (s *Server) index(ctx context.Context, args *indexArgs) (state indexState,
 	return indexStateSuccess, nil
 }
 
+// reportIndexFailureToSourcegraph sends the error message of a failed index
+// attempt to Sourcegraph via UpdateIndexStatus so it can be persisted.
+// Any error is logged but not propagated — this is best-effort.
+func reportIndexFailureToSourcegraph(args *indexArgs, sg Sourcegraph, indexErr error, logger sglog.Logger) {
+	status := []indexStatus{{
+		RepoID:         args.RepoID,
+		LastIndexError: indexErr.Error(),
+		// Branches and IndexTimeUnix intentionally zero:
+		// the index did not complete so there is no new shard data.
+	}}
+	if err := sg.UpdateIndexStatus(status); err != nil {
+		logger.Error("failed to report index failure to sourcegraph",
+			sglog.String("repo", args.Name),
+			sglog.Uint32("id", args.RepoID),
+			sglog.Error(err),
+		)
+	}
+}
+
 // updateIndexStatusOnSourcegraph pushes the current state to sourcegraph so
 // it can update the zoekt_repos table.
 func updateIndexStatusOnSourcegraph(c gitIndexConfig, args *indexArgs, sg Sourcegraph) error {
diff --git a/cmd/zoekt-sourcegraph-indexserver/sg.go b/cmd/zoekt-sourcegraph-indexserver/sg.go
index da9b4e2ec..8ebef8601 100644
--- a/cmd/zoekt-sourcegraph-indexserver/sg.go
+++ b/cmd/zoekt-sourcegraph-indexserver/sg.go
@@ -369,9 +369,10 @@ func (s *sourcegraphClient) listRepoIDs(ctx context.Context, indexed []uint32) (
 }
 
 type indexStatus struct {
-	RepoID        uint32
-	Branches      []zoekt.RepositoryBranch
-	IndexTimeUnix int64
+	RepoID         uint32
+	Branches       []zoekt.RepositoryBranch
+	IndexTimeUnix  int64
+	LastIndexError string
 }
 
 type updateIndexStatusRequest struct {
@@ -392,9 +393,10 @@ func (u *updateIndexStatusRequest) ToProto() *configv1.UpdateIndexStatusRequest
 		}
 
 		repositories = append(repositories, &configv1.UpdateIndexStatusRequest_Repository{
-			RepoId:        repo.RepoID,
-			Branches:      branches,
-			IndexTimeUnix: repo.IndexTimeUnix,
+			RepoId:         repo.RepoID,
+			Branches:       branches,
+			IndexTimeUnix:  repo.IndexTimeUnix,
+			LastIndexError: repo.LastIndexError,
 		})
 	}
 
@@ -419,9 +421,10 @@ func (u *updateIndexStatusRequest) FromProto(x *configv1.UpdateIndexStatusReques
 		}
 
 		repositories = append(repositories, indexStatus{
-			RepoID:        repo.GetRepoId(),
-			Branches:      branches,
-			IndexTimeUnix: repo.GetIndexTimeUnix(),
+			RepoID:         repo.GetRepoId(),
+			Branches:       branches,
+			IndexTimeUnix:  repo.GetIndexTimeUnix(),
+			LastIndexError: repo.GetLastIndexError(),
 		})
 	}