diff --git a/cores/esp8266/Arduino.h b/cores/esp8266/Arduino.h
index 12286db86..0264aeac0 100644
--- a/cores/esp8266/Arduino.h
+++ b/cores/esp8266/Arduino.h
@@ -249,6 +249,8 @@ void optimistic_yield(uint32_t interval_us);
 
 using std::min;
 using std::max;
+using std::isinf;
+using std::isnan;
 
 #define _min(a,b) ((a)<(b)?(a):(b))
 #define _max(a,b) ((a)>(b)?(a):(b))