diff --git a/src/nvim/grid_defs.h b/src/nvim/grid_defs.h
index 9e588d0387..ce90886978 100644
--- a/src/nvim/grid_defs.h
+++ b/src/nvim/grid_defs.h
@@ -11,7 +11,7 @@
 
 // The characters and attributes drawn on grids.
 typedef char_u schar_T[(MAX_MCO+1) * 4 + 1];
-typedef int16_t sattr_T;
+typedef int sattr_T;
 
 /// ScreenGrid represents a resizable rectuangular grid displayed by UI clients.
 ///
diff --git a/src/nvim/highlight.c b/src/nvim/highlight.c
index 093cc4923b..2783a327b2 100644
--- a/src/nvim/highlight.c
+++ b/src/nvim/highlight.c
@@ -90,7 +90,12 @@ static int get_attr_entry(HlEntry entry)
     }
   }
 
-  id = (int)kv_size(attr_entries);
+  size_t next_id = kv_size(attr_entries);
+  if (next_id > INT_MAX) {
+    ELOG("The index on attr_entries has overflowed");
+    return 0;
+  }
+  id = (int)next_id;
   kv_push(attr_entries, entry);
 
   map_put(HlEntry, int)(attr_entry_ids, entry, id);