1 files changed, 2 insertions, 0 deletions
diff --git a/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs b/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
index dcdbcf74..f7dc8aa8 100644
--- a/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
+++ b/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
@@ -33,7 +33,9 @@ namespace StardewModdingAPI.Toolkit.Serialization.Models
         *********/
         /// <summary>Normalize whitespace in a raw string.</summary>
         /// <param name="input">The input to strip.</param>
+#if NET5_0_OR_GREATER
         [return: NotNullIfNotNull("input")]
+#endif
         private string? NormalizeWhitespace(string? input)
         {
             return input?.Trim();