diff --git a/.changeset/new-mails-prove.md b/.changeset/new-mails-prove.md
new file mode 100644
index 0000000000..06c5a36521
--- /dev/null
+++ b/.changeset/new-mails-prove.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where using .nullish() in a formdata Astro action would always parse as a string
diff --git a/packages/astro/src/actions/runtime/virtual/server.ts b/packages/astro/src/actions/runtime/virtual/server.ts
index 326bbf4f9b..3efa7ca149 100644
--- a/packages/astro/src/actions/runtime/virtual/server.ts
+++ b/packages/astro/src/actions/runtime/virtual/server.ts
@@ -124,8 +124,8 @@ export function formDataToObject<T extends z.AnyZodObject>(
 	const obj: Record<string, unknown> = {};
 	for (const [key, baseValidator] of Object.entries(schema.shape)) {
 		let validator = baseValidator;
-		if (baseValidator instanceof z.ZodOptional || baseValidator instanceof z.ZodNullable) {
-			validator = baseValidator._def.innerType;
+		while (validator instanceof z.ZodOptional || validator instanceof z.ZodNullable) {
+			validator = validator._def.innerType;
 		}
 		if (validator instanceof z.ZodBoolean) {
 			obj[key] = formData.has(key);