diff --git a/bin/find-device-port-freebsd b/bin/find-device-port-freebsd
new file mode 100755
index 00000000..afe08934
--- /dev/null
+++ b/bin/find-device-port-freebsd
@@ -0,0 +1,24 @@
+#!/usr/bin/env perl
+
+use warnings;
+use strict;
+
+#
+# Scan all USB devices to find the Model 01's modem device number.
+#
+my @output = qx(/usr/sbin/usbconfig show_ifdrv);
+my $serial_port_number;
+
+foreach my $line (@output) {
+  chomp $line;
+
+  next unless $line =~ m/umodem(\d+):.*Keyboardio Model 01/;
+  $serial_port_number = $1;
+}
+
+die "Can't find Model 01" unless defined($serial_port_number);
+
+my $serial_port_name = "/dev/cuaU$serial_port_number";
+die "Missing serial port at $serial_port_name" unless -e $serial_port_name;
+print "$serial_port_name\n";
+exit 0;
diff --git a/bin/kaleidoscope-builder b/bin/kaleidoscope-builder
index 52c83ff1..66e44e85 100755
--- a/bin/kaleidoscope-builder
+++ b/bin/kaleidoscope-builder
@@ -45,15 +45,24 @@ firmware_size () {
     ## This is a terrible hack, please don't hurt me. - algernon
 
     find_max_prog_size
-    output="$("$@" | grep "\\(Program\\|Data\\):" | sed -e 's,^,  - ,' && echo)"
+    set +e
+    raw_output=$("$@" 2> /dev/null)
+    rc=$?
+    set -e
 
-    PROGSIZE="$(echo "${output}" | grep "Program:" | cut -d: -f2 | awk '{print $1}')"
+    if [ $rc -eq 0 ]; then
+        output="$(echo "${raw_output}"| grep "\\(Program\\|Data\\):" | sed -e 's,^,  - ,' && echo)"
 
-    PERCENT="$(echo "${PROGSIZE}" "${MAX_PROG_SIZE}" | awk "{ printf \"%02.01f\", \$1 / \$2 * 100 }")"
+        PROGSIZE="$(echo "${output}" | grep "Program:" | cut -d: -f2 | awk '{print $1}')"
 
-    # we want the sed there, doing with shell builtins would be worse.
-    # shellcheck disable=SC2001 disable=SC1117
-    echo "${output}" | sed -e "s/\(Program:.*\)(\([0-9\.]*%\) Full)/\1(${PERCENT}% Full)/"
+        PERCENT="$(echo "${PROGSIZE}" "${MAX_PROG_SIZE}" | awk "{ printf \"%02.01f\", \$1 / \$2 * 100 }")"
+
+        # we want the sed there, doing with shell builtins would be worse.
+        # shellcheck disable=SC2001 disable=SC1117
+        echo "${output}" | sed -e "s/\(Program:.*\)(\([0-9\.]*%\) Full)/\1(${PERCENT}% Full)/"
+    else
+        echo "Unable to determine image size."
+    fi
 }
 
 
@@ -102,7 +111,7 @@ flash () {
     ${preFlash_HOOKS}
 
     reset_device
-    sleep 3s
+    sleep 3
     find_bootloader_ports
     check_bootloader_port_and_flash
 
@@ -121,7 +130,7 @@ check_bootloader_port_and_flash () {
 }
 
 flash_over_usb () {
-    sleep 1s
+    sleep 1
     ${AVRDUDE} -q -q -C "${AVRDUDE_CONF}" -p"${MCU}" -cavr109 -D -P "${DEVICE_PORT_BOOTLOADER}" -b57600 "-Uflash:w:${HEX_FILE_PATH}:i"
 }
 
@@ -283,7 +292,7 @@ size () {
     fi
 
     echo "- Size: firmware/${LIBRARY}/${OUTPUT_FILE_PREFIX}.elf"
-    firmware_size "${AVR_SIZE}" -C --mcu="${MCU}" "${ELF_FILE_PATH}"
+    firmware_size "${AVR_SIZE}" "${AVR_SIZE_FLAGS}" "${ELF_FILE_PATH}"
     echo
 }
 
diff --git a/etc/kaleidoscope-builder.conf b/etc/kaleidoscope-builder.conf
index 37eb70a0..26f205a1 100644
--- a/etc/kaleidoscope-builder.conf
+++ b/etc/kaleidoscope-builder.conf
@@ -98,6 +98,31 @@ if [ "${uname_S}" = "Darwin" ]; then
 	DEVICE_PORT_BOOTLOADER="$(perl ${DEVICE_PORT_PROBER})"
     }
 
+elif [ "${uname_S}" = "FreeBSD" ]; then
+
+    find_device_port() {
+	DIR=$(dirname "$0")
+	DEVICE_PORT_PROBER="${DIR}/find-device-port-freebsd"
+	DEVICE_PORT="$(perl ${DEVICE_PORT_PROBER})"
+    }
+
+    reset_device_cmd() {
+	/bin/stty -f ${DEVICE_PORT} 1200
+    }
+
+    MD5="md5"
+    AVR_SIZE="${AVR_SIZE:-/usr/local/bin/avr-size}"
+    AVR_NM="${AVR_NM:-/usr/local/bin/avr-nm}"
+    AVR_OBJDUMP="${AVR_OBJDUMP:-/usr/local/bin/avr-objdump}"
+    AVRDUDE="${AVRDUDE:-/usr/local/bin/avrdude}"
+    AVRDUDE_CONF="${AVRDUDE_CONF:-/usr/local/etc/avrdude.conf}"
+
+    find_bootloader_ports() {
+	DIR=$(dirname "$0")
+	DEVICE_PORT_PROBER="${DIR}/find-device-port-freebsd"
+	DEVICE_PORT_BOOTLOADER="$(perl ${DEVICE_PORT_PROBER})"
+    }
+
 fi
 
 ######
@@ -117,6 +142,7 @@ ARDUINO_IDE_VERSION="10607"
 ######
 
 AVR_SIZE="${AVR_SIZE:-${ARDUINO_TOOLS_PATH}/avr/bin/avr-size}"
+AVR_SIZE_FLAGS="${AVR_SIZE_FLAGS:--C --mcu=${MCU}}"
 AVR_NM="${AVR_NM:-${ARDUINO_TOOLS_PATH}/avr/bin/avr-nm}"
 AVR_OBJDUMP="${AVR_OBJDUMP:-${ARDUINO_TOOLS_PATH}/avr/bin/avr-objdump}"
 AVRDUDE="${AVRDUDE:-${ARDUINO_TOOLS_PATH}/avr/bin/avrdude}"