diff --git a/cluster/gce/util.sh b/cluster/gce/util.sh
index c8a54b0adf..6f99ff48b9 100755
--- a/cluster/gce/util.sh
+++ b/cluster/gce/util.sh
@@ -1913,5 +1913,14 @@ function prepare-e2e() {
 # limits the size of metadata fields to 32K, and stripping comments is the
 # easiest way to buy us a little more room.
 function prepare-startup-script() {
-  sed '/^\s*#\([^!].*\)*$/ d' ${KUBE_ROOT}/cluster/gce/configure-vm.sh > ${KUBE_TEMP}/configure-vm.sh
+  # Find a standard sed instance (and ensure that the command works as expected on a Mac).
+  SED=sed
+  if which gsed &>/dev/null; then
+    SED=gsed
+  fi
+  if ! ($SED --version 2>&1 | grep -q GNU); then
+    echo "!!! GNU sed is required.  If on OS X, use 'brew install gnu-sed'."
+    exit 1
+  fi
+  $SED '/^\s*#\([^!].*\)*$/ d' ${KUBE_ROOT}/cluster/gce/configure-vm.sh > ${KUBE_TEMP}/configure-vm.sh
 }