diff --git a/Adafruit_MQTT.cpp b/Adafruit_MQTT.cpp
index 2cd1d1c..9cb0898 100644
--- a/Adafruit_MQTT.cpp
+++ b/Adafruit_MQTT.cpp
@@ -21,7 +21,7 @@
 // SOFTWARE.
 #include "Adafruit_MQTT.h"
 
-#ifndef dtostrf
+#ifdef ARDUINO_SAMD_ZERO
 static char *dtostrf (double val, signed char width, unsigned char prec, char *sout) {
   char fmt[20];
   sprintf(fmt, "%%%d.%df", width, prec);