diff --git a/.changeset/pretty-oranges-heal.md b/.changeset/pretty-oranges-heal.md
new file mode 100644
index 000000000000..f1b8b38e0bc3
--- /dev/null
+++ b/.changeset/pretty-oranges-heal.md
@@ -0,0 +1,5 @@
+---
+"astro": patch
+---
+
+Adds an error message for non-string transition:name values
diff --git a/packages/astro/src/runtime/server/transition.ts b/packages/astro/src/runtime/server/transition.ts
index ec33e1eae482..755e64417ac2 100644
--- a/packages/astro/src/runtime/server/transition.ts
+++ b/packages/astro/src/runtime/server/transition.ts
@@ -91,6 +91,9 @@ export function renderTransition(
 	animationName: TransitionAnimationValue | undefined,
 	transitionName: string
 ) {
+	if (typeof (transitionName ?? '') !== 'string') {
+		throw new Error(`Invalid transition name {${transitionName}}`);
+	}
 	// Default to `fade` (similar to `initial`, but snappier)
 	if (!animationName) animationName = 'fade';
 	const scope = createTransitionScope(result, hash);