diff --git a/R/stat-smooth.r b/R/stat-smooth.r
index ad9b438967..6dc63cc647 100644
--- a/R/stat-smooth.r
+++ b/R/stat-smooth.r
@@ -25,7 +25,9 @@
 #' @param level Level of confidence interval to use (0.95 by default).
 #' @param span Controls the amount of smoothing for the default loess smoother.
 #'   Smaller numbers produce wigglier lines, larger numbers produce smoother
-#'   lines.
+#'   lines. Only used with loess, i.e. when `method = "loess"`,
+#'   or when `method = NULL` (the default) and there are fewer than 1,000
+#'   observations.
 #' @param n Number of points at which to evaluate smoother.
 #' @param method.args List of additional arguments passed on to the modelling
 #'   function defined by `method`.
diff --git a/man/geom_smooth.Rd b/man/geom_smooth.Rd
index 95c11217cb..afff989f46 100644
--- a/man/geom_smooth.Rd
+++ b/man/geom_smooth.Rd
@@ -120,7 +120,9 @@ the default plot specification, e.g. \code{\link[=borders]{borders()}}.}
 
 \item{span}{Controls the amount of smoothing for the default loess smoother.
 Smaller numbers produce wigglier lines, larger numbers produce smoother
-lines.}
+lines. Only used with loess, i.e. when \code{method = "loess"},
+or when \code{method = NULL} (the default) and there are fewer than 1,000
+observations.}
 
 \item{fullrange}{Should the fit span the full range of the plot, or just
 the data?}