diff --git a/.changeset/hip-bottles-hide.md b/.changeset/hip-bottles-hide.md
new file mode 100644
index 000000000000..d8564ab649e9
--- /dev/null
+++ b/.changeset/hip-bottles-hide.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Added warning message when using unsupported file extensions in pages/
diff --git a/packages/astro/src/core/routing/manifest/create.ts b/packages/astro/src/core/routing/manifest/create.ts
index 47282210990a..51f495e8b468 100644
--- a/packages/astro/src/core/routing/manifest/create.ts
+++ b/packages/astro/src/core/routing/manifest/create.ts
@@ -229,6 +229,8 @@ export function createRouteManifest(
 	const localFs = fsMod ?? nodeFs;
 	const isPrenderDefault = isHybridOutput(settings.config);
 
+	const foundInvalidFileExtensions: Set<string> = new Set();
+
 	function walk(
 		fs: typeof nodeFs,
 		dir: string,
@@ -252,6 +254,11 @@ export function createRouteManifest(
 			}
 			// filter out "foo.astro_tmp" files, etc
 			if (!isDir && !validPageExtensions.has(ext) && !validEndpointExtensions.has(ext)) {
+				if (!foundInvalidFileExtensions.has(ext)) {
+					foundInvalidFileExtensions.add(ext);
+					warn(logging, 'astro', `Invalid file extension for Pages: ${ext}`);
+				}
+
 				return;
 			}
 			const segment = isDir ? basename : name;