diff --git a/quartz/plugins/emitters/aliases.ts b/quartz/plugins/emitters/aliases.ts
index 0eb4f3a..9cb9bd5 100644
--- a/quartz/plugins/emitters/aliases.ts
+++ b/quartz/plugins/emitters/aliases.ts
@@ -1,4 +1,4 @@
-import { isRelativeURL, resolveRelative, simplifySlug } from "../../util/path"
+import { FullSlug, isRelativeURL, resolveRelative, simplifySlug } from "../../util/path"
 import { QuartzEmitterPlugin } from "../types"
 import { write } from "./helpers"
 import { BuildCtx } from "../../util/ctx"
@@ -9,9 +9,11 @@ async function* processFile(ctx: BuildCtx, file: VFile) {
   const ogSlug = simplifySlug(file.data.slug!)
 
   for (const aliasTarget of file.data.aliases ?? []) {
-    const aliasTargetSlug = isRelativeURL(aliasTarget)
-      ? path.normalize(path.join(ogSlug, "..", aliasTarget))
-      : aliasTarget
+    const aliasTargetSlug = (
+      isRelativeURL(aliasTarget)
+        ? path.normalize(path.join(ogSlug, "..", aliasTarget))
+        : aliasTarget
+    ) as FullSlug
 
     const redirUrl = resolveRelative(aliasTargetSlug, ogSlug)
     yield write({