diff --git a/letsencrypt-auto-source/letsencrypt-auto b/letsencrypt-auto-source/letsencrypt-auto
index 9be546584..d96836e64 100755
--- a/letsencrypt-auto-source/letsencrypt-auto
+++ b/letsencrypt-auto-source/letsencrypt-auto
@@ -175,6 +175,10 @@ BootstrapDebCommon() {
   augeas_pkg="libaugeas0 augeas-lenses"
   AUGVERSION=`apt-cache show --no-all-versions libaugeas0 | grep ^Version: | cut -d" " -f2`
 
+  if [ "$ASSUME_YES" = 1 ]; then
+    YES_FLAG="-y"
+  fi
+
   AddBackportRepo() {
       # ARGS:
       BACKPORT_NAME="$1"
@@ -196,7 +200,7 @@ BootstrapDebCommon() {
               $SUDO apt-get update
           fi
       fi
-      $SUDO apt-get install -y --no-install-recommends -t "$BACKPORT_NAME" $augeas_pkg
+      $SUDO apt-get install $YES_FLAG --no-install-recommends -t "$BACKPORT_NAME" $augeas_pkg
       augeas_pkg=
 
   }
@@ -215,7 +219,7 @@ BootstrapDebCommon() {
       # XXX add a case for ubuntu PPAs
   fi
 
-  $SUDO apt-get install -y --no-install-recommends \
+  $SUDO apt-get install $YES_FLAG --no-install-recommends \
     python \
     python-dev \
     $virtualenv \
@@ -334,8 +338,12 @@ BootstrapArchCommon() {
   # pacman -T exits with 127 if there are missing dependencies
   missing=$($SUDO pacman -T $deps) || true
 
+  if [ "$ASSUME_YES" = 1 ]; then
+    noconfirm="--noconfirm"
+  fi
+
   if [ "$missing" ]; then
-    $SUDO pacman -S --needed $missing
+    $SUDO pacman -S --needed $missing $noconfirm
   fi
 }
 
diff --git a/letsencrypt-auto-source/pieces/bootstrappers/arch_common.sh b/letsencrypt-auto-source/pieces/bootstrappers/arch_common.sh
index b2fc01a14..39e2da5fe 100755
--- a/letsencrypt-auto-source/pieces/bootstrappers/arch_common.sh
+++ b/letsencrypt-auto-source/pieces/bootstrappers/arch_common.sh
@@ -21,7 +21,11 @@ BootstrapArchCommon() {
   # pacman -T exits with 127 if there are missing dependencies
   missing=$($SUDO pacman -T $deps) || true
 
+  if [ "$ASSUME_YES" = 1 ]; then
+    noconfirm="--noconfirm"
+  fi
+
   if [ "$missing" ]; then
-    $SUDO pacman -S --needed $missing
+    $SUDO pacman -S --needed $missing $noconfirm
   fi
 }
diff --git a/letsencrypt-auto-source/pieces/bootstrappers/deb_common.sh b/letsencrypt-auto-source/pieces/bootstrappers/deb_common.sh
index 57ed11399..b2b76fd55 100644
--- a/letsencrypt-auto-source/pieces/bootstrappers/deb_common.sh
+++ b/letsencrypt-auto-source/pieces/bootstrappers/deb_common.sh
@@ -34,6 +34,10 @@ BootstrapDebCommon() {
   augeas_pkg="libaugeas0 augeas-lenses"
   AUGVERSION=`apt-cache show --no-all-versions libaugeas0 | grep ^Version: | cut -d" " -f2`
 
+  if [ "$ASSUME_YES" = 1 ]; then
+    YES_FLAG="-y"
+  fi
+
   AddBackportRepo() {
       # ARGS:
       BACKPORT_NAME="$1"
@@ -55,7 +59,7 @@ BootstrapDebCommon() {
               $SUDO apt-get update
           fi
       fi
-      $SUDO apt-get install -y --no-install-recommends -t "$BACKPORT_NAME" $augeas_pkg
+      $SUDO apt-get install $YES_FLAG --no-install-recommends -t "$BACKPORT_NAME" $augeas_pkg
       augeas_pkg=
 
   }
@@ -74,7 +78,7 @@ BootstrapDebCommon() {
       # XXX add a case for ubuntu PPAs
   fi
 
-  $SUDO apt-get install -y --no-install-recommends \
+  $SUDO apt-get install $YES_FLAG --no-install-recommends \
     python \
     python-dev \
     $virtualenv \