diff --git a/CHANGELOG.md b/CHANGELOG.md
index 87d99a96..72d6cb7b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@
 
 - Drop Python 3.9 support, require Python >= 3.10 ({pr}`1044`, {user}`benjeffery`)
 
+- Remove overzealous derived state validation in C API. ({pr}`1059`, {user}`benjeffery`)
+
+
 ## [0.4.1] - 2024-04-19
 
 ** Changes **
diff --git a/lib/tree_sequence_builder.c b/lib/tree_sequence_builder.c
index 3463c4df..9f6ed1bd 100644
--- a/lib/tree_sequence_builder.c
+++ b/lib/tree_sequence_builder.c
@@ -423,7 +423,7 @@ tree_sequence_builder_add_mutation(
         ret = TSI_ERR_BAD_MUTATION_SITE;
         goto out;
     }
-    if (derived_state < 0 || derived_state >= (allele_t) self->sites.num_alleles[site]) {
+    if (derived_state < 0) {
         ret = TSI_ERR_BAD_MUTATION_DERIVED_STATE;
         goto out;
     }