diff --git a/dsl/attribute.go b/dsl/attribute.go
index 75f7408701..ba4adce7ae 100644
--- a/dsl/attribute.go
+++ b/dsl/attribute.go
@@ -229,13 +229,13 @@ func OneOf(name string, args ...any) {
 	}
 	fn, ok := args[len(args)-1].(func())
 	if !ok {
-		eval.ReportError("OneOf: last argument must be a function")
+		eval.InvalidArgError("function", args[len(args)-1])
 	}
 	var desc string
 	if len(args) > 1 {
 		desc, ok = args[0].(string)
 		if !ok {
-			eval.ReportError("OneOf: description must be a string")
+			eval.InvalidArgError("string", args[0])
 		}
 	}
 	Attribute(name, &expr.Union{TypeName: name}, desc, fn)
diff --git a/eval/eval_test.go b/eval/eval_test.go
index d74c0c33e1..bfda376449 100644
--- a/eval/eval_test.go
+++ b/eval/eval_test.go
@@ -20,6 +20,8 @@ func TestInvalidArgError(t *testing.T) {
 		"ErrorName (int)":      {func() { Type("name", func() { ErrorName(1, 2) }) }, "cannot use 2 (type int) as type name"},
 		"Example":              {func() { Example(1, 2) }, "cannot use 1 (type int) as type summary (string)"},
 		"Headers":              {func() { Headers(1) }, "cannot use 1 (type int) as type function"},
+		"OneOf (function)":     {func() { Type("name", func() { OneOf("name", "description", 1) }) }, "cannot use 1 (type int) as type function"},
+		"OneOf (string)":       {func() { Type("name", func() { OneOf("name", 1, func() {}) }) }, "cannot use 1 (type int) as type string"},
 		"Param":                {func() { API("name", func() { HTTP(func() { Params(1) }) }) }, "cannot use 1 (type int) as type function"},
 		"Response":             {func() { Service("s", func() { HTTP(func() { Response(1) }) }) }, "cannot use 1 (type int) as type name of error"},
 		"ResultType":           {func() { ResultType("identifier", 1) }, "cannot use 1 (type int) as type function or string"},