diff --git a/bin/find-device-port-linux-udev b/bin/find-device-port-linux-udev
index 79201857..0e284c37 100644
--- a/bin/find-device-port-linux-udev
+++ b/bin/find-device-port-linux-udev
@@ -2,14 +2,27 @@
 
 use warnings;
 use strict;
+
+use FindBin qw{$Bin};
+
+die "Usage: $0 VID PID\n" unless @ARGV == 2;
+
 my $vid    = shift;
 my $pid    = shift;
 my $prefix = '/dev/serial/by-id/';
 my @paths  = `ls $prefix`;
 my %devices;
 
+sub debug {
+    print STDERR @_;
+}
+
+debug "Looking for USB device with vid=$vid and pid=$pid\n";
+
 for my $path (@paths) {
     chomp($path);
+    debug "Examining $path\n";
+    debug "  not symlink\n" unless -l $prefix . $path;
     next unless -l $prefix . $path;
     my @data = `udevadm info -q property --name=${prefix}${path}`;
     for my $line (@data) {
@@ -17,15 +30,36 @@ for my $path (@paths) {
         my ( $key, $val ) = split( /=/, $line, 2 );
         $devices{$path}{$key} = $val;
     }
-    if (   ( hex $devices{$path}{'ID_VENDOR_ID'} == hex $vid )
-        && ( hex $devices{$path}{'ID_MODEL_ID'} == hex $pid ) )
-    {
+    if ( hex $devices{$path}{'ID_VENDOR_ID'} != hex $vid ) {
+        debug "  ID_VENDOR_ID $devices{$path}{'ID_VENDOR_ID'} != $vid\n";
+        next;
+    }
+    if ( hex $devices{$path}{'ID_MODEL_ID'} != hex $pid ) {
+        debug "  ID_MODEL_ID $devices{$path}{'ID_MODEL_ID'} != $pid\n";
+        next;
+    }
 
-        if ( $devices{$path}{'ID_MM_CANDIDATE'} ) {
-            warn "Yikes. ModemManager wants to pwn your keyboard";
-        }
+    debug "  Found keyboard!\n";
 
-        print $devices{$path}{DEVNAME};
-        exit(0);
+    if ( $devices{$path}{'ID_MM_DEVICE_IGNORE'} ) {
+        debug "  ID_MM_DEVICE_IGNORE is set - good!\n";
     }
+
+    if ( $devices{$path}{'ID_MM_CANDIDATE'}) {
+      my $rules = "$Bin/../etc/99-kaleidoscope.rules";
+      debug <<EOWARN
+
+WARNING: your udev rules are currently configured to suggest
+that your keyboard is suitable for use by ModemManager.  This
+means that there is a risk of ModemManager interfering.  To avoid
+this, copy
+
+    $rules
+
+to /etc/udev/rules.d
+EOWARN
+    }
+
+    print $devices{$path}{DEVNAME};
+    exit(0);
 }
diff --git a/bin/kaleidoscope-builder b/bin/kaleidoscope-builder
index 4bf28ffb..c95cfb88 100755
--- a/bin/kaleidoscope-builder
+++ b/bin/kaleidoscope-builder
@@ -249,13 +249,47 @@ reset_device() {
 }
 
 check_device_port () {
-    if [ -z $DEVICE_PORT ]; then
-        echo "Couldn't autodetect the keyboard's serial port."
-        echo "If you see this message and your keyboard is connected to your computer,"
-        echo "it probably means that our serial port detection logic is buggy or incomplete."
-        echo
-        echo "Please report this issue at https://github.com/keyboardio/Kaleidoscope";
-        exit 0;
+    if [ -z "$DEVICE_PORT" ]; then
+        cat <<EOF >&2
+Couldn't autodetect the keyboard's serial port.
+If you see this message and your keyboard is connected to your computer,
+it probably means that our serial port detection logic is buggy or incomplete.
+
+Please report this issue at https://github.com/keyboardio/Kaleidoscope
+EOF
+        exit 1
+    elif echo "$DEVICE_PORT" | grep -q '[[:space:]]'; then
+        cat <<EOF >&2
+Unexpected whitespace found in detected serial port:
+
+    $DEVICE_PORT
+
+If you see this message, it means that our serial port
+detection logic is buggy or incomplete.
+
+Please report this issue at https://github.com/keyboardio/Kaleidoscope
+EOF
+        exit 1
+    fi
+
+    if ! [ -w "$DEVICE_PORT" ]; then
+        cat <<EOF >&2
+
+$DEVICE_PORT is not writable:
+
+  `ls -l $DEVICE_PORT`
+
+You are currently in the following groups:
+
+  `id -Gn`
+
+Please ensure you have followed the instructions on setting up your
+account to be in the right group:
+
+https://github.com/keyboardio/Kaleidoscope/wiki/Install-Arduino-support-on-Linux
+
+EOF
+        exit 1
     fi
 }
 
diff --git a/etc/99-kaleidoscope.rules b/etc/99-kaleidoscope.rules
index cae399b2..c69b9053 100644
--- a/etc/99-kaleidoscope.rules
+++ b/etc/99-kaleidoscope.rules
@@ -1,4 +1,2 @@
-SUBSYSTEMS=="usb", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="2300", SYMLINK+="model01", ENV{ID_MM_DEVICE_IGNORE}="1"
-SUBSYSTEMS=="usb", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="2301", SYMLINK+="model01", ENV{ID_MM_DEVICE_IGNORE}="1"
-
-
+SUBSYSTEMS=="usb", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="2300", SYMLINK+="model01", ENV{ID_MM_DEVICE_IGNORE}:="1", ENV{ID_MM_CANDIDATE}:="0"
+SUBSYSTEMS=="usb", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="2301", SYMLINK+="model01", ENV{ID_MM_DEVICE_IGNORE}:="1", ENV{ID_MM_CANDIDATE}:="0"