diff --git a/.changeset/fix-optional-repeated-protobuf.md b/.changeset/fix-optional-repeated-protobuf.md
new file mode 100644
index 0000000..f04ca74
--- /dev/null
+++ b/.changeset/fix-optional-repeated-protobuf.md
@@ -0,0 +1,5 @@
+---
+"@codama/renderers-vixen-parser": patch
+---
+
+- Fix broken protobuf generation for optional vectors in IDL.
\ No newline at end of file
diff --git a/src/getProtoTypeManifestVisitor.ts b/src/getProtoTypeManifestVisitor.ts
index bb0cadc..154f78a 100644
--- a/src/getProtoTypeManifestVisitor.ts
+++ b/src/getProtoTypeManifestVisitor.ts
@@ -304,6 +304,9 @@ export function getProtoTypeManifestVisitor(options: {
 
                     const optionPrefix = resolveNestedTypeNode(optionType.prefix);
                     if (optionPrefix.format === 'u8' && optionPrefix.endian === 'le') {
+                        if (childManifest.type.startsWith('repeated ')) {
+                            return childManifest;
+                        }
                         return {
                             ...childManifest,
                             type: `optional ${childManifest.type}`,
diff --git a/src/getRenderMapVisitor.ts b/src/getRenderMapVisitor.ts
index c2d35cc..00e5efb 100644
--- a/src/getRenderMapVisitor.ts
+++ b/src/getRenderMapVisitor.ts
@@ -207,14 +207,24 @@ function getOptionTypeTransform(
     const innerTransform = getTransform(item, outerTypeName, idlDefinedTypes, options);
     const cleanedTransform = innerTransform.replace(`self.${outerTypeName}`, 'x');
 
+    let returnTransform = '';
     switch (cleanedTransform) {
         case 'x':
-            return `self.${outerTypeName}`;
+            returnTransform = `self.${outerTypeName}`;
+            break;
         case 'Some(x.into_proto())':
-            return `self.${outerTypeName}.map(|x| x.into_proto())`;
+            returnTransform = `self.${outerTypeName}.map(|x| x.into_proto())`;
+            break;
         default:
-            return `self.${outerTypeName}.map(|x| ${cleanedTransform})`;
+            returnTransform = `self.${outerTypeName}.map(|x| ${cleanedTransform})`;
+            break;
     }
+
+    if (item.kind === 'arrayTypeNode' || item.kind === 'fixedSizeTypeNode') {
+        returnTransform += '.unwrap_or_default()';
+    }
+
+    return returnTransform;
 }
 
 function getTransform(