diff --git a/cmd/zoekt-git-index/main.go b/cmd/zoekt-git-index/main.go
index 8aff1fbcc..cde395800 100644
--- a/cmd/zoekt-git-index/main.go
+++ b/cmd/zoekt-git-index/main.go
@@ -46,6 +46,7 @@ func run() int {
 	deltaShardNumberFallbackThreshold := flag.Uint64("delta_threshold", 0, "upper limit on the number of preexisting shards that can exist before attempting a delta build (0 to disable fallback behavior)")
 	languageMap := flag.String("language_map", "", "a mapping between a language and its ctags processor (a:0,b:3).")
 	tenantID := flag.Int("tenant_id", 0, "tenant ID to use for indexed repositories")
+	repoID := flag.Uint("repo_id", 0, "opaque ID to use for indexed repositories. Surfaces as `RepositoryID` in the REST search response.")
 
 	cpuProfile := flag.String("cpuprofile", "", "write cpu profile to `file`")
 
@@ -77,6 +78,7 @@ func run() int {
 	opts := cmd.OptionsFromFlags()
 	opts.IsDelta = *isDelta
 	opts.RepositoryDescription.TenantID = *tenantID
+	opts.RepositoryDescription.ID = uint32(*repoID)
 
 	var branches []string
 	if *branchesStr != "" {
diff --git a/gitindex/index.go b/gitindex/index.go
index f35af7357..6f30574b0 100644
--- a/gitindex/index.go
+++ b/gitindex/index.go
@@ -251,8 +251,11 @@ func setTemplatesFromConfig(desc *zoekt.Repository, repoDir string) error {
 		}
 	}
 
-	id, _ := strconv.ParseUint(sec.Options.Get("repoid"), 10, 32)
-	desc.ID = uint32(id)
+	idString := sec.Options.Get("repoid")
+	if idString != "" {
+		id, _ := strconv.ParseUint(idString, 10, 32)
+		desc.ID = uint32(id)
+	}
 
 	if desc.RawConfig == nil {
 		desc.RawConfig = map[string]string{}