diff --git a/NAMESPACE b/NAMESPACE
index f315ec2..d79ffef 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -101,6 +101,8 @@ importFrom(ggplot2,is.ggplot)
 importFrom(ggplot2,is.theme)
 importFrom(ggplot2,labs)
 importFrom(ggplot2,margin)
+importFrom(ggplot2,max_height)
+importFrom(ggplot2,max_width)
 importFrom(ggplot2,panel_cols)
 importFrom(ggplot2,panel_rows)
 importFrom(ggplot2,scale_x_continuous)
@@ -140,6 +142,7 @@ importFrom(gtable,gtable_add_rows)
 importFrom(gtable,gtable_height)
 importFrom(gtable,gtable_width)
 importFrom(gtable,is.gtable)
+importFrom(stats,ave)
 importFrom(stats,na.omit)
 importFrom(utils,as.roman)
 importFrom(utils,modifyList)
diff --git a/R/collect_axes.R b/R/collect_axes.R
index 952e34b..114f905 100644
--- a/R/collect_axes.R
+++ b/R/collect_axes.R
@@ -136,6 +136,7 @@ collect_axes <- function(gt, dir = "x") {
 # For every given row, check if all non-zero grobs occupying that row have a
 # name that has a pattern. If all these grobs in that row do, measure the
 # grob heights and put that into the gtable's heights.
+#' @importFrom ggplot2 max_height
 retrofit_rows <- function(gt, rows, pattern = NULL) {
   if (is.null(pattern) || length(rows) == 0) {
     return(gt)
@@ -166,6 +167,7 @@ retrofit_rows <- function(gt, rows, pattern = NULL) {
 # For every given column, check if all non-zero grobs occupying that column
 # have a name that has a pattern. If all these grobs in that column do, measure
 # the grob widths and put that into the gtable's widths.
+#' @importFrom ggplot2 max_width
 retrofit_cols <- function(gt, cols, pattern = NULL) {
   if (is.null(pattern) || length(cols) == 0) {
     return(gt)
@@ -240,6 +242,7 @@ is_zero <- function(x) {
 }
 
 # Determine uniqueness of grobs
+#' @importFrom stats ave
 grob_id <- function(grobs, layout, byrow, merge = FALSE) {
 
   # Hash the grobs to determine unique grobs
diff --git a/R/inset_element.R b/R/inset_element.R
index 79e27e3..2ba4d88 100644
--- a/R/inset_element.R
+++ b/R/inset_element.R
@@ -35,9 +35,11 @@
 #' # Grobs and other objects can be added as insets as well
 #' p1 + inset_element(grid::circleGrob(), 0.4, 0.4, 0.6, 0.6)
 #'
-#' logo <- system.file('help', 'figures', 'logo.png', package = 'patchwork')
-#' logo <- png::readPNG(logo, native = TRUE)
-#' p1 + inset_element(logo, 0.8, 0.8, 1, 1, align_to = 'full')
+#' if (requireNamespace('png', quietly = TRUE)) {
+#'   logo <- system.file('help', 'figures', 'logo.png', package = 'patchwork')
+#'   logo <- png::readPNG(logo, native = TRUE)
+#'   p1 + inset_element(logo, 0.8, 0.8, 1, 1, align_to = 'full')
+#' }
 #'
 #' # Just as expected insets are still amenable to changes after the fact
 #' p1 +
diff --git a/man/inset_element.Rd b/man/inset_element.Rd
index 23d71aa..1f6f498 100644
--- a/man/inset_element.Rd
+++ b/man/inset_element.Rd
@@ -57,9 +57,11 @@ p1 + inset_element(p2, 0, 0.6, 0.4, 1, align_to = 'full')
 # Grobs and other objects can be added as insets as well
 p1 + inset_element(grid::circleGrob(), 0.4, 0.4, 0.6, 0.6)
 
-logo <- system.file('help', 'figures', 'logo.png', package = 'patchwork')
-logo <- png::readPNG(logo, native = TRUE)
-p1 + inset_element(logo, 0.8, 0.8, 1, 1, align_to = 'full')
+if (requireNamespace('png', quietly = TRUE)) {
+  logo <- system.file('help', 'figures', 'logo.png', package = 'patchwork')
+  logo <- png::readPNG(logo, native = TRUE)
+  p1 + inset_element(logo, 0.8, 0.8, 1, 1, align_to = 'full')
+}
 
 # Just as expected insets are still amenable to changes after the fact
 p1 +
diff --git a/man/plot_layout.Rd b/man/plot_layout.Rd
index 979dc3d..894e479 100644
--- a/man/plot_layout.Rd
+++ b/man/plot_layout.Rd
@@ -14,7 +14,7 @@ plot_layout(
   tag_level = NULL,
   design = NULL,
   axes = NULL,
-  axis_titles = NULL
+  axis_titles = axes
 )
 }
 \arguments{