diff --git a/DESCRIPTION b/DESCRIPTION
index 7a625b9..6e65578 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -12,12 +12,15 @@ Description: Some helpful extensions and modifications to the 'ggplot2'
     package name, which stands for Claus O. Wilke's plot library.
 URL: https://github.com/wilkelab/cowplot
 Depends:
-    R (>= 3.0.0),
-    ggplot2 (>= 1.0.0)
+    R (>= 3.2.0),
+    ggplot2 (>= 1.0.0),
 Imports:
     grid (>= 3.0.0),
     gtable (>= 0.1.2),
-    plyr (>= 1.8.2)
+    plyr (>= 1.8.2),
+    grDevices,
+    methods,
+    utils
 License: GPL-2
 LazyData: true
 Suggests:
diff --git a/R/draw.R b/R/draw.R
index c2489ab..84aeb2e 100644
--- a/R/draw.R
+++ b/R/draw.R
@@ -6,7 +6,7 @@
 # ****** Internal functions used by drawing code ******
 ggplot_to_gtable <- function(plot)
 {
-  if (is(plot, "ggplot")){
+  if (methods::is(plot, "ggplot")){
     ggplot2::ggplotGrob(plot)
   }
   else if (is(plot, "gtable")){
diff --git a/R/save.R b/R/save.R
index 67e1a1d..88902bf 100644
--- a/R/save.R
+++ b/R/save.R
@@ -25,7 +25,7 @@
 #' @export
 ggsave <- function(filename = NULL, plot = ggplot2::last_plot(),
                    device = default_device(filename), path = NULL, scale = 1,
-                   width = par("din")[1], height = par("din")[2], units = c("in", "cm", "mm"),
+                   width = graphics::par("din")[1], height = graphics::par("din")[2], units = c("in", "cm", "mm"),
                    dpi = 300, limitsize = TRUE, ...) {
   # this code is copied directly from ggplot2. ugly, but
   # the only way to implement this properly.
@@ -109,7 +109,7 @@ ggsave <- function(filename = NULL, plot = ggplot2::last_plot(),
     filename <- file.path(path, filename)
   }
   device(file=filename, width=width, height=height, ...)
-  on.exit(capture.output(dev.off()))
+  on.exit(utils::capture.output(grDevices::dev.off()))
   print(plot)
 
   invisible()
diff --git a/man/ggsave.Rd b/man/ggsave.Rd
index 7a642b2..1c12aaf 100644
--- a/man/ggsave.Rd
+++ b/man/ggsave.Rd
@@ -6,8 +6,8 @@
 \usage{
 ggsave(filename = NULL, plot = ggplot2::last_plot(),
   device = default_device(filename), path = NULL, scale = 1,
-  width = par("din")[1], height = par("din")[2], units = c("in", "cm",
-  "mm"), dpi = 300, limitsize = TRUE, ...)
+  width = graphics::par("din")[1], height = graphics::par("din")[2],
+  units = c("in", "cm", "mm"), dpi = 300, limitsize = TRUE, ...)
 }
 \arguments{
 \item{filename}{Filename of plot}