diff --git a/src/MemoryPack.Generator/DiagnosticDescriptors.cs b/src/MemoryPack.Generator/DiagnosticDescriptors.cs
index 50a77087..1af8b9ab 100644
--- a/src/MemoryPack.Generator/DiagnosticDescriptors.cs
+++ b/src/MemoryPack.Generator/DiagnosticDescriptors.cs
@@ -120,7 +120,7 @@ internal static class DiagnosticDescriptors
     public static readonly DiagnosticDescriptor UnionMemberNotAllowStruct = new(
         id: "MEMPACK015",
         title: "Union member can't be struct",
-        messageFormat: "The MemoryPackable object '{0}' union member '{1}' can't be member, not allows struct",
+        messageFormat: "The MemoryPackable object '{0}' union member '{1}' can't be member, not allow struct",
         category: Category,
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true);