diff --git a/tools/cmd/gen-types/types.ts.tmpl b/tools/cmd/gen-types/types.ts.tmpl
index 55fee850d..0814d75f7 100644
--- a/tools/cmd/gen-types/types.ts.tmpl
+++ b/tools/cmd/gen-types/types.ts.tmpl
@@ -10,7 +10,7 @@ import { encodeAs } from "../encoding";
 {{  define "objectify"}}
 this.{{lcName .Name}} &&
 {{-   if .Repeatable -}}
-this.{{lcName .Name}}?.map(v => {{objectify . "v"}})
+this.{{lcName .Name}}?.map(v => v == undefined ? undefined : {{objectify . "v"}})
 {{-   else}}
 {{objectify . (print "this." (lcName .Name))}}
 {{-   end}}
diff --git a/tools/cmd/gen-types/typescript.go b/tools/cmd/gen-types/typescript.go
index 114ee3e71..8d6903c20 100644
--- a/tools/cmd/gen-types/typescript.go
+++ b/tools/cmd/gen-types/typescript.go
@@ -62,7 +62,7 @@ func TsNeedsCtor(typ *Type) bool {
 func TsResolveType(field *Field) string {
 	typ := field.Type.TypescriptType(false)
 	if field.Repeatable {
-		typ = typ + "[]"
+		typ = "(" + typ + " | undefined)[]"
 	}
 	return typ
 }
@@ -84,7 +84,7 @@ func TsInputType(field *Field) string {
 		typ = field.Type.TypescriptInputType(false)
 	}
 	if field.Repeatable {
-		typ = "(" + typ + ")[]"
+		typ = "(" + typ + " | undefined)[]"
 	}
 	return typ
 }
@@ -117,7 +117,7 @@ func TsUnobjectify(field *Field, varName string) string {
 		return tsUnobjectify2(field, varName)
 	}
 
-	return fmt.Sprintf("%s.map(v => %s)", varName, tsUnobjectify2(field, "v"))
+	return fmt.Sprintf("%s.map(v => v == undefined ? undefined : %s)", varName, tsUnobjectify2(field, "v"))
 }
 
 func tsUnobjectify2(field *Field, varName string) string {