diff --git a/.travis.yml b/.travis.yml
index 51c18e1..84192a7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@ install:
 - pip install -U platformio
 - platformio update
 script:
-- platformio run -e $PLATOFORMIO_ENVIRONMENT
+- platformio run --verbose --environment $PLATOFORMIO_ENVIRONMENT
 - mv .pio/build/${PLATOFORMIO_ENVIRONMENT}/firmware.elf teensytoany-${PLATOFORMIO_ENVIRONMENT}.elf
 - mv .pio/build/${PLATOFORMIO_ENVIRONMENT}/firmware.hex teensytoany-${PLATOFORMIO_ENVIRONMENT}.hex
 - cp teensytoany-${PLATOFORMIO_ENVIRONMENT}.elf teensytoany-${PLATOFORMIO_ENVIRONMENT}-${TRAVIS_BRANCH}.elf
diff --git a/src/i2c.cpp b/src/i2c.cpp
index 76c2d71..5a5d4e9 100644
--- a/src/i2c.cpp
+++ b/src/i2c.cpp
@@ -1,7 +1,6 @@
 #include "i2c.hpp"
 #include <errno.h>
-// Teensy 3.0
-#if defined(__arm__) && defined(TEENSYDUINO) && defined(KINETISK)
+#if TEENSY_TO_ANY_HAS_I2C
 #include <i2c_t3.h>
 int I2CMaster::init(int baudrate, int timeout_ms, int address_size,
                     int address_msb_first) {
diff --git a/src/i2c.hpp b/src/i2c.hpp
index 15e50c8..9ea91aa 100644
--- a/src/i2c.hpp
+++ b/src/i2c.hpp
@@ -1,6 +1,17 @@
 #pragma once
-#if defined(__arm__) && defined(TEENSYDUINO) && defined(KINETISK)
-#define HAS_I2C 1
+// only support teensies 3.1, 3.2, 3.5, and 3.6
+// See list of microcontroller units
+// https://docs.platformio.org/en/latest/platforms/teensy.html
+#if defined(TEENSYDUINO) && \
+    (defined(__MK20DX256__) || defined(__MK64FX512__) || \
+     defined(__MK66FX1M0__))
+#define TEENSY_TO_ANY_HAS_I2C 1
+#else
+#define TEENSY_TO_ANY_HAS_I2C 0
+#warning I2C library not available for this build.
+#endif
+
+#if TEENSY_TO_ANY_HAS_I2C
 #include <unistd.h>
 
 class I2CMaster {
@@ -22,6 +33,4 @@ class I2CMaster {
   bool is_initialized = false;
   bool slave_8bit_address = true;
 };
-#else
-#define HAS_I2C 0
 #endif
diff --git a/src/main.cpp b/src/main.cpp
index 7a73a4c..a9969f3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -28,7 +28,7 @@ inline SPISettings my_spi_settings() {
   return SPISettings(spi_baudrate, spi_bit_order, spi_data_mode);
 }
 
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
 I2CMaster i2c;
 #endif
 
@@ -71,7 +71,7 @@ int version_func(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_init(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   int baudrate = 100'000;
   int timeout_ms = 200'000; // 200ms
   int address_size = 2;
@@ -96,7 +96,7 @@ int i2c_init(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_reset(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   return i2c.reset();
 #else
   return -1;
@@ -104,7 +104,7 @@ int i2c_reset(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_write_uint16(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 4)
     return EINVAL;
 
@@ -118,7 +118,7 @@ int i2c_write_uint16(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_write_uint8(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 4)
     return EINVAL;
 
@@ -133,7 +133,7 @@ int i2c_write_uint8(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_read_uint16(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 3)
     return EINVAL;
 
@@ -153,7 +153,7 @@ int i2c_read_uint16(CommandRouter *cmd, int argc, const char **argv) {
 }
 
 int i2c_read_uint8(CommandRouter *cmd, int argc, const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 3)
     return EINVAL;
 
@@ -173,7 +173,7 @@ int i2c_read_uint8(CommandRouter *cmd, int argc, const char **argv) {
 
 int i2c_read_no_register_uint8(CommandRouter *cmd, int argc,
                                const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 2)
     return EINVAL;
 
@@ -193,7 +193,7 @@ int i2c_read_no_register_uint8(CommandRouter *cmd, int argc,
 
 int i2c_write_no_register_uint8(CommandRouter *cmd, int argc,
                                 const char **argv) {
-#if HAS_I2C
+#if TEENSY_TO_ANY_HAS_I2C
   if (argc != 3)
     return EINVAL;