diff --git a/sql/multi_range_read.cc b/sql/multi_range_read.cc
index c72c92889f5..7d859a71e50 100644
--- a/sql/multi_range_read.cc
+++ b/sql/multi_range_read.cc
@@ -1122,7 +1122,7 @@ bool DsMrr_impl::setup_buffer_sharing(uint key_size_in_keybuf,
      (ulonglong2double(rowids_size) + key_buff_elem_size));
 
   size_t bytes_for_rowids= 
-    round(fraction_for_rowids * (full_buf_end - full_buf));
+    (size_t)round(fraction_for_rowids * (full_buf_end - full_buf));
   
   long bytes_for_keys= (full_buf_end - full_buf) - bytes_for_rowids;
 
diff --git a/sql/multi_range_read.h b/sql/multi_range_read.h
index a22ef0fef61..07e6295a021 100644
--- a/sql/multi_range_read.h
+++ b/sql/multi_range_read.h
@@ -346,7 +346,14 @@ private:
   /* TRUE <=> index_reader->refill_buffer() call has returned EOF */
   bool index_reader_exhausted;
   
+  /* 
+    TRUE <=> We should call index_reader->refill_buffer(). This happens if
+    1. we've made index_reader->get_next() call which returned EOF
+    2. we haven't made any index_reader calls (and our first call should 
+       be index_reader->refill_buffer(initial=TRUE)
+  */
   bool index_reader_needs_refill;
+
   /* TRUE <=> need range association, buffers hold {rowid, range_id} pairs */
   bool is_mrr_assoc;