diff --git a/R/geom-bar.R b/R/geom-bar.R
index e4611fbabb..03f2c76ba3 100644
--- a/R/geom-bar.R
+++ b/R/geom-bar.R
@@ -129,6 +129,8 @@ geom_bar <- function(mapping = NULL, data = NULL,
 GeomBar <- ggproto("GeomBar", GeomRect,
   required_aes = c("x", "y"),
 
+  optional_aes = character(),
+
   # These aes columns are created by setup_data(). They need to be listed here so
   # that GeomRect$handle_na() properly removes any bars that fall outside the defined
   # limits, not just those for which x and y are outside the limits