diff --git a/server/internal/handler/github.go b/server/internal/handler/github.go
index 1091778bab..e459dcdd29 100644
--- a/server/internal/handler/github.go
+++ b/server/internal/handler/github.go
@@ -581,8 +581,12 @@ func (h *Handler) ListPullRequestsForIssue(w http.ResponseWriter, r *http.Reques
 // because branch names are conventionally lowercase but issue prefixes are
 // uppercase. Word boundary on the left prevents matching inside email-style
 // strings (e.g. "abc@MUL-1") and the digit anchor on the right rules out
-// version numbers like "v1.2-3".
-var identifierRe = regexp.MustCompile(`(?i)\b([a-z][a-z0-9]{0,6})-(\d+)\b`)
+// version numbers like "v1.2-3". The key group allows up to 9 chars (not the
+// Space key's 7-char cap) because legacy issue_prefix values up to 10 chars
+// still resolve via the issue_identifier_alias backfill (see migration 134);
+// extraction only needs to find a candidate, the DB lookup (current key,
+// then alias) decides validity.
+var identifierRe = regexp.MustCompile(`(?i)\b([a-z][a-z0-9]{0,9})-(\d+)\b`)
 
 // closingIdentifierRe extracts identifiers that appear immediately after a
 // GitHub-style closing keyword ("close[sd]?", "fix(e[sd])?", "resolve[sd]?"),
@@ -594,7 +598,7 @@ var identifierRe = regexp.MustCompile(`(?i)\b([a-z][a-z0-9]{0,6})-(\d+)\b`)
 // title prefixes like "MUL-1: ..." link the PR (via identifierRe) but
 // never auto-close.
 var closingIdentifierRe = regexp.MustCompile(
-	`(?i)\b(?:close[sd]?|fix(?:e[sd])?|resolve[sd]?)[:\s]+([a-z][a-z0-9]{0,6})-(\d+)\b`,
+	`(?i)\b(?:close[sd]?|fix(?:e[sd])?|resolve[sd]?)[:\s]+([a-z][a-z0-9]{0,9})-(\d+)\b`,
 )
 
 // HandleGitHubWebhook (POST /api/webhooks/github) is GitHub's destination for
diff --git a/server/migrations/134_issue_identifier_alias.up.sql b/server/migrations/134_issue_identifier_alias.up.sql
index 107624f3d6..7d1fbc245c 100644
--- a/server/migrations/134_issue_identifier_alias.up.sql
+++ b/server/migrations/134_issue_identifier_alias.up.sql
@@ -14,3 +14,23 @@ CREATE TABLE issue_identifier_alias (
 );
 
 CREATE INDEX idx_issue_identifier_alias_issue ON issue_identifier_alias(issue_id);
+
+-- Backfill aliases for the renaming migration 131 already performed. 131
+-- normalized every workspace's legacy issue_prefix into a Space key
+-- satisfying ^[A-Z][A-Z0-9]{0,6}$ (uppercase, strip non-alnum, truncate to 7).
+-- Legacy prefixes longer than 7 chars, digit-first, or punctuated therefore
+-- diverge from the key their issues now resolve under, and — unlike a
+-- runtime move-to-space — that rename never went through the alias-writing
+-- path above, since no issue actually changed space_id. Old links/CLI/GitHub
+-- references using the pre-migration prefix would otherwise 404 forever.
+-- workspace.issue_prefix is untouched by 131/132 (kept intentionally; see
+-- 132's header comment), so the original value is still available here.
+INSERT INTO issue_identifier_alias (workspace_id, space_key_lower, number, issue_id)
+SELECT i.workspace_id, lower(btrim(w.issue_prefix)), i.number, i.id
+FROM issue i
+JOIN workspace w ON w.id = i.workspace_id
+JOIN workspace_space wt ON wt.id = i.space_id
+WHERE w.issue_prefix IS NOT NULL
+  AND btrim(w.issue_prefix) <> ''
+  AND lower(btrim(w.issue_prefix)) <> lower(wt.key)
+ON CONFLICT DO NOTHING;