diff --git a/Project.toml b/Project.toml
index 97820274b..66b42a0e3 100644
--- a/Project.toml
+++ b/Project.toml
@@ -35,7 +35,7 @@ Colors = "0.9"
 Compose = "0.7"
 Contour = "0.5"
 CoupledFields = "0.1"
-DataFrames = "0.15, 0.16, 0.17, 0.18, 0.19"
+DataFrames = "0.15, 0.16, 0.17, 0.18, 0.19, 0.20"
 DataStructures = "0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17"
 Distributions = "0.16, 0.17, 0.18, 0.19, 0.20, 0.21"
 DocStringExtensions = "0.7, 0.8"
diff --git a/src/Gadfly.jl b/src/Gadfly.jl
index e2e4a1fd3..3c814df2b 100755
--- a/src/Gadfly.jl
+++ b/src/Gadfly.jl
@@ -515,7 +515,7 @@ function render_prepare(plot::Plot)
         map(s->(s, _theme(l, plot)), collect(stats))
     end
 
-    for element in flatten(([(s, plot.theme) for s in plot.statistics],
+    for element in Iterators.flatten(([(s, plot.theme) for s in plot.statistics],
                          [(l.geom, _theme(plot, l)) for l in plot.layers],
                          layer_stats_with_theme...))
 
@@ -563,7 +563,7 @@ function render_prepare(plot::Plot)
         (haskey(plot.mapping, var) || haskey(scales, var)) && continue
 
         t = :categorical
-        for data in flatten((datas, subplot_datas))
+        for data in Iterators.flatten((datas, subplot_datas))
             val = getfield(data, var)
             if val != nothing && val != :categorical
                 t = classify_data(val)
diff --git a/src/data.jl b/src/data.jl
index c32ad50e6..d8334b016 100644
--- a/src/data.jl
+++ b/src/data.jl
@@ -66,7 +66,7 @@ function chain(ds::Data...)
         if isempty(vs)
             setfield!(chained_data, name, nothing)
         else
-            setfield!(chained_data, name, flatten(vs))
+            setfield!(chained_data, name, Iterators.flatten(vs))
         end
     end
 
diff --git a/src/geom/boxplot.jl b/src/geom/boxplot.jl
index 1b9264cd4..b99fc3b7d 100644
--- a/src/geom/boxplot.jl
+++ b/src/geom/boxplot.jl
@@ -121,7 +121,7 @@ function render(geom::BoxplotGeometry, theme::Gadfly.Theme, aes::Gadfly.Aestheti
 
     # Outliers
     if !geom.suppress_outliers && aes.outliers != nothing && !isempty(aes.outliers)
-        xys = collect(flatten(zip(cycle([x]), ys, cycle([c]))
+        xys = collect(Iterators.flatten(zip(cycle([x]), ys, cycle([c]))
                              for (x, ys, c) in zip(xs, aes.outliers, cs)))
         compose!(ctx, (context(),
             Shape.circle([x for (x, y, c) in xys], [y for (x, y, c) in xys], [theme.point_size], to), svgclass("marker"),
diff --git a/src/geom/ribbon.jl b/src/geom/ribbon.jl
index 5f6f27a99..a25384415 100644
--- a/src/geom/ribbon.jl
+++ b/src/geom/ribbon.jl
@@ -55,8 +55,8 @@ function render(geom::RibbonGeometry, theme::Gadfly.Theme, aes::Gadfly.Aesthetic
     end
 
     kys = keys(max_points)
-    polys = [collect(Tuple{XT, YT}, flatten((min_points[k], max_points[k]))) for k in kys]
-    lines = [collect(Tuple{XT, YT}, flatten((min_points[k], [(last(min_points[k])[1], NaN)], max_points[k]))) for k in kys]
+    polys = [collect(Tuple{XT, YT}, Iterators.flatten((min_points[k], max_points[k]))) for k in kys]
+    lines = [collect(Tuple{XT, YT}, Iterators.flatten((min_points[k], [(last(min_points[k])[1], NaN)], max_points[k]))) for k in kys]
 
     n = length(kys)
     colors = Vector{Union{Colorant, String}}(undef, n)
diff --git a/src/scale.jl b/src/scale.jl
index 9388f558e..7cb2b3921 100644
--- a/src/scale.jl
+++ b/src/scale.jl
@@ -622,7 +622,7 @@ const color_continuous_gradient = color_continuous  ### WHY HAVE THIS ALIAS?
 
 function apply_scale(scale::ContinuousColorScale,
                      aess::Vector{Gadfly.Aesthetics}, datas::Gadfly.Data...)
-    cdata = skipmissing(flatten(i.color for i in datas if i.color != nothing))
+    cdata = skipmissing(Iterators.flatten(i.color for i in datas if i.color != nothing))
     if !isempty(cdata)
       cmin, cmax = extrema(cdata)
     else
diff --git a/src/statistics.jl b/src/statistics.jl
index 7d890b39a..6b303ce75 100644
--- a/src/statistics.jl
+++ b/src/statistics.jl
@@ -851,7 +851,7 @@ function apply_statistic(stat::TickStatistic,
 
     isempty(in_vals) && return
 
-    in_vals = flatten(in_vals)
+    in_vals = Iterators.flatten(in_vals)
 
     # consider forced tick marks
     if stat.ticks != :auto