diff --git a/buf/registry/module/v1/label_service.proto b/buf/registry/module/v1/label_service.proto
index 6263a55..2b2d5bf 100644
--- a/buf/registry/module/v1/label_service.proto
+++ b/buf/registry/module/v1/label_service.proto
@@ -147,6 +147,7 @@ message ListLabelHistoryRequest {
   // or it may be a Commit id.
   //
   // If a Commit id, the returned history will start at that Commit.
+  // It is an error to provide a Commit id that doesn't exist on the Label.
   //
   // If empty, the first page is returned.
   string page_token = 2 [(buf.validate.field).string.max_len = 4096];
diff --git a/buf/registry/module/v1beta1/label_service.proto b/buf/registry/module/v1beta1/label_service.proto
index 86a69c0..f82c45e 100644
--- a/buf/registry/module/v1beta1/label_service.proto
+++ b/buf/registry/module/v1beta1/label_service.proto
@@ -148,6 +148,7 @@ message ListLabelHistoryRequest {
   // or it may be a Commit id.
   //
   // If a Commit id, the returned history will start at that Commit.
+  // It is an error to provide a Commit id that doesn't exist on the Label.
   //
   // If empty, the first page is returned.
   string page_token = 2 [(buf.validate.field).string.max_len = 4096];