diff --git a/.changeset/bright-pants-trade.md b/.changeset/bright-pants-trade.md
new file mode 100644
index 0000000000..00267ad71b
--- /dev/null
+++ b/.changeset/bright-pants-trade.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix JPEG image size determination
diff --git a/packages/astro/src/assets/utils/vendor/image-size/types/jpg.ts b/packages/astro/src/assets/utils/vendor/image-size/types/jpg.ts
index 1ccf2d99f1..763cfc98c0 100644
--- a/packages/astro/src/assets/utils/vendor/image-size/types/jpg.ts
+++ b/packages/astro/src/assets/utils/vendor/image-size/types/jpg.ts
@@ -122,7 +122,8 @@ export const JPG: IImage = {
 
       // Every JPEG block must begin with a 0xFF
       if (input[i] !== 0xff) {
-        input = input.slice(1)
+        // Change from upstream: fix non-0xFF blocks skipping
+        input = input.slice(i)
         continue
       }