diff --git a/flat_mutation_reader.hh b/flat_mutation_reader.hh
index 1ec196b39e..736724c992 100644
--- a/flat_mutation_reader.hh
+++ b/flat_mutation_reader.hh
@@ -810,16 +810,23 @@ flat_mutation_reader make_nonforwardable(flat_mutation_reader, bool);
 
 flat_mutation_reader make_empty_flat_reader(schema_ptr s, reader_permit permit);
 
+// Mutation vector cannot be empty, all mutations should have the same schema.
 flat_mutation_reader flat_mutation_reader_from_mutations(reader_permit permit, std::vector<mutation>,
         const dht::partition_range& pr = query::full_partition_range, streamed_mutation::forwarding fwd = streamed_mutation::forwarding::no);
+
+// Mutation vector cannot be empty, all mutations should have the same schema.
 inline flat_mutation_reader flat_mutation_reader_from_mutations(reader_permit permit, std::vector<mutation> ms, streamed_mutation::forwarding fwd) {
     return flat_mutation_reader_from_mutations(std::move(permit), std::move(ms), query::full_partition_range, fwd);
 }
+
+// Mutation vector cannot be empty, all mutations should have the same schema.
 flat_mutation_reader
 flat_mutation_reader_from_mutations(reader_permit permit,
                                     std::vector<mutation> ms,
                                     const query::partition_slice& slice,
                                     streamed_mutation::forwarding fwd = streamed_mutation::forwarding::no);
+
+// Mutation vector cannot be empty, all mutations should have the same schema.
 flat_mutation_reader
 flat_mutation_reader_from_mutations(reader_permit permit,
                                     std::vector<mutation> ms,