diff --git a/quartz/plugins/transformers/lastmod.ts b/quartz/plugins/transformers/lastmod.ts
index 015c350a..7deeefb0 100644
--- a/quartz/plugins/transformers/lastmod.ts
+++ b/quartz/plugins/transformers/lastmod.ts
@@ -2,6 +2,7 @@ import fs from "fs"
 import path from "path"
 import { Repository } from "@napi-rs/simple-git"
 import { QuartzTransformerPlugin } from "../types"
+import chalk from "chalk"
 
 export interface Options {
   priority: ("frontmatter" | "git" | "filesystem")[]
@@ -11,9 +12,18 @@ const defaultOptions: Options = {
   priority: ["frontmatter", "git", "filesystem"],
 }
 
-function coerceDate(d: any): Date {
+function coerceDate(fp: string, d: any): Date {
   const dt = new Date(d)
-  return isNaN(dt.getTime()) ? new Date() : dt
+  const invalidDate = isNaN(dt.getTime())
+  if (invalidDate && d !== undefined) {
+    console.log(
+      chalk.yellow(
+        `\nWarning: found invalid date "${d}" in \`${fp}\`. Supported formats: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#date_time_string_format`,
+      ),
+    )
+  }
+
+  return invalidDate ? new Date() : dt
 }
 
 type MaybeDate = undefined | string | number
@@ -32,10 +42,11 @@ export const CreatedModifiedDate: QuartzTransformerPlugin<Partial<Options> | und
             let modified: MaybeDate = undefined
             let published: MaybeDate = undefined
 
-            const fp = path.posix.join(file.cwd, file.data.filePath as string)
+            const fp = file.data.filePath!
+            const fullFp = path.posix.join(file.cwd, fp)
             for (const source of opts.priority) {
               if (source === "filesystem") {
-                const st = await fs.promises.stat(fp)
+                const st = await fs.promises.stat(fullFp)
                 created ||= st.birthtimeMs
                 modified ||= st.mtimeMs
               } else if (source === "frontmatter" && file.data.frontmatter) {
@@ -54,9 +65,9 @@ export const CreatedModifiedDate: QuartzTransformerPlugin<Partial<Options> | und
             }
 
             file.data.dates = {
-              created: coerceDate(created),
-              modified: coerceDate(modified),
-              published: coerceDate(published),
+              created: coerceDate(fp, created),
+              modified: coerceDate(fp, modified),
+              published: coerceDate(fp, published),
             }
           }
         },