diff --git a/CHANGELOG.md b/CHANGELOG.md
index de6f0831..cdd02587 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,11 @@
 ArduinoJson: change log
 =======================
 
+HEAD
+----
+
+* Fixed build when another lib does `#undef isnan` (issue #284)
+
 v5.6.1
 ------
 
diff --git a/include/ArduinoJson/Internals/JsonWriter.hpp b/include/ArduinoJson/Internals/JsonWriter.hpp
index ba6da82f..5df2e68f 100644
--- a/include/ArduinoJson/Internals/JsonWriter.hpp
+++ b/include/ArduinoJson/Internals/JsonWriter.hpp
@@ -8,8 +8,7 @@
 #pragma once
 
 #include "../Polyfills/attributes.hpp"
-#include "../Polyfills/isInfinity.hpp"
-#include "../Polyfills/isNaN.hpp"
+#include "../Polyfills/math.hpp"
 #include "../Polyfills/normalize.hpp"
 #include "../Print.hpp"
 #include "Encoding.hpp"
@@ -33,18 +32,34 @@ class JsonWriter {
   // Returns the number of bytes sent to the Print implementation.
   // This is very handy for implementations of printTo() that must return the
   // number of bytes written.
-  size_t bytesWritten() const { return _length; }
+  size_t bytesWritten() const {
+    return _length;
+  }
 
-  void beginArray() { writeRaw('['); }
-  void endArray() { writeRaw(']'); }
+  void beginArray() {
+    writeRaw('[');
+  }
+  void endArray() {
+    writeRaw(']');
+  }
 
-  void beginObject() { writeRaw('{'); }
-  void endObject() { writeRaw('}'); }
+  void beginObject() {
+    writeRaw('{');
+  }
+  void endObject() {
+    writeRaw('}');
+  }
 
-  void writeColon() { writeRaw(':'); }
-  void writeComma() { writeRaw(','); }
+  void writeColon() {
+    writeRaw(':');
+  }
+  void writeComma() {
+    writeRaw(',');
+  }
 
-  void writeBoolean(bool value) { writeRaw(value ? "true" : "false"); }
+  void writeBoolean(bool value) {
+    writeRaw(value ? "true" : "false");
+  }
 
   void writeString(const char *value) {
     if (!value) {
@@ -132,8 +147,12 @@ class JsonWriter {
     }
   }
 
-  void writeRaw(const char *s) { _length += _sink.print(s); }
-  void writeRaw(char c) { _length += _sink.write(c); }
+  void writeRaw(const char *s) {
+    _length += _sink.print(s);
+  }
+  void writeRaw(char c) {
+    _length += _sink.write(c);
+  }
 
  protected:
   Print &_sink;
diff --git a/include/ArduinoJson/Polyfills/isNaN.hpp b/include/ArduinoJson/Polyfills/isNaN.hpp
deleted file mode 100644
index cc378143..00000000
--- a/include/ArduinoJson/Polyfills/isNaN.hpp
+++ /dev/null
@@ -1,54 +0,0 @@
-// Copyright Benoit Blanchon 2014-2016
-// MIT License
-//
-// Arduino JSON library
-// https://github.com/bblanchon/ArduinoJson
-// If you like this project, please add a star!
-
-#pragma once
-
-// If Visual Studo <= 2012
-#if defined(_MSC_VER) && _MSC_VER <= 1700
-#include <float.h>
-#else
-#include <math.h>
-#endif
-
-// GCC warning: "conversion to 'float' from 'double' may alter its value"
-#ifdef __GNUC__
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
-#pragma GCC diagnostic push
-#endif
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
-#pragma GCC diagnostic ignored "-Wfloat-conversion"
-#else
-#pragma GCC diagnostic ignored "-Wconversion"
-#endif
-#endif
-
-namespace ArduinoJson {
-namespace Polyfills {
-
-// If Visual Studo <= 2012
-#if defined(_MSC_VER) && _MSC_VER <= 1700
-
-template <typename T>
-bool isNaN(T x) {
-  return _isnan(x) != 0;
-}
-#else
-
-template <typename T>
-bool isNaN(T x) {
-  return isnan(x);
-}
-
-#endif
-}
-}
-
-#if defined(__GNUC__)
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
-#pragma GCC diagnostic pop
-#endif
-#endif
diff --git a/include/ArduinoJson/Polyfills/isInfinity.hpp b/include/ArduinoJson/Polyfills/math.hpp
similarity index 62%
rename from include/ArduinoJson/Polyfills/isInfinity.hpp
rename to include/ArduinoJson/Polyfills/math.hpp
index be1f9fa8..b26f6a48 100644
--- a/include/ArduinoJson/Polyfills/isInfinity.hpp
+++ b/include/ArduinoJson/Polyfills/math.hpp
@@ -9,10 +9,26 @@
 
 // If Visual Studo <= 2012
 #if defined(_MSC_VER) && _MSC_VER <= 1700
+
 #include <float.h>
+
+namespace ArduinoJson {
+namespace Polyfills {
+template <typename T>
+bool isNaN(T x) {
+  return _isnan(x) != 0;
+}
+
+template <typename T>
+bool isInfinity(T x) {
+  return !_finite(x);
+}
+}
+}
+
 #else
+
 #include <math.h>
-#endif
 
 // GCC warning: "conversion to 'float' from 'double' may alter its value"
 #ifdef __GNUC__
@@ -26,40 +42,42 @@
 #endif
 #endif
 
+// Workaround for libs that #undef isnan or isinf
+// https://github.com/bblanchon/ArduinoJson/issues/284
+#if !defined(isnan) || !defined(isinf)
+namespace std {}
+#endif
+
 namespace ArduinoJson {
 namespace Polyfills {
 
-// If Visual Studo <= 2012
-#if defined(_MSC_VER) && _MSC_VER <= 1700
 template <typename T>
-bool isInfinity(T x) {
-  return !_finite(x);
+bool isNaN(T x) {
+// Workaround for libs that #undef isnan
+// https://github.com/bblanchon/ArduinoJson/issues/284
+#ifndef isnan
+  using namespace std;
+#endif
+
+  return isnan(x);
 }
-#else
+
 template <typename T>
 bool isInfinity(T x) {
+// Workaround for libs that #undef isinf
+// https://github.com/bblanchon/ArduinoJson/issues/284
+#ifndef isinf
+  using namespace std;
+#endif
+
   return isinf(x);
 }
 
-#if defined(_GLIBCXX_HAVE_ISINFL) && _GLIBCXX_HAVE_ISINFL
-template <>
-inline bool isInfinity<double>(double x) {
-  return isinfl(x);
-}
-#endif
-
-#if defined(_GLIBCXX_HAVE_ISINFF) && _GLIBCXX_HAVE_ISINFF
-template <>
-inline bool isInfinity<float>(float x) {
-  return isinff(x);
-}
-#endif
-#endif
-}
-}
-
 #if defined(__GNUC__)
 #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
 #pragma GCC diagnostic pop
 #endif
 #endif
+}
+}
+#endif