diff --git a/projects/plugins/jetpack/changelog/fix-jetpack-slideshow-aspectRatio-fallback b/projects/plugins/jetpack/changelog/fix-jetpack-slideshow-aspectRatio-fallback
new file mode 100644
index 000000000000..a1362228d50b
--- /dev/null
+++ b/projects/plugins/jetpack/changelog/fix-jetpack-slideshow-aspectRatio-fallback
@@ -0,0 +1,4 @@
+Significance: patch
+Type: bugfix
+
+Slideshow: Ensure slideshows do not stretch to parent container width on mobile if no list height is set.
diff --git a/projects/plugins/jetpack/extensions/blocks/slideshow/swiper-callbacks.js b/projects/plugins/jetpack/extensions/blocks/slideshow/swiper-callbacks.js
index 9245b5ed89d4..49cff5102a0b 100644
--- a/projects/plugins/jetpack/extensions/blocks/slideshow/swiper-callbacks.js
+++ b/projects/plugins/jetpack/extensions/blocks/slideshow/swiper-callbacks.js
@@ -47,7 +47,8 @@ function swiperResize( swiper ) {
 	if ( ! img ) {
 		return;
 	}
-	const aspectRatio = img.naturalWidth / img.naturalHeight;
+	const hasNatural = img.naturalWidth > 0 && img.naturalHeight > 0;
+	const aspectRatio = hasNatural ? img.naturalWidth / img.naturalHeight : SIXTEEN_BY_NINE;
 	const sanityAspectRatio = Math.max( Math.min( aspectRatio, SIXTEEN_BY_NINE ), 1 );
 	const sanityHeight =
 		typeof window !== 'undefined'