diff --git a/Dapper/SqlMapper.cs b/Dapper/SqlMapper.cs
index 5575a6f5f..350b55cb3 100644
--- a/Dapper/SqlMapper.cs
+++ b/Dapper/SqlMapper.cs
@@ -446,8 +446,9 @@ public static void SetDbType(IDataParameter parameter, object value)
         {
             handler = null;
             var nullUnderlyingType = Nullable.GetUnderlyingType(type);
-            if (nullUnderlyingType is not null) type = nullUnderlyingType;
-            if (type.IsEnum && !typeMap.ContainsKey(type))
+
+            if (nullUnderlyingType is not  null) type = nullUnderlyingType;
+            if (type.IsEnum && !typeMap.ContainsKey(type) && !typeHandlers.ContainsKey(type))
             {
                 type = Enum.GetUnderlyingType(type);
             }