diff --git a/mfbt/decimal/moz-decimal-utils.h b/mfbt/decimal/moz-decimal-utils.h
index d05447c1b477..6a9d8038de5e 100644
--- a/mfbt/decimal/moz-decimal-utils.h
+++ b/mfbt/decimal/moz-decimal-utils.h
@@ -38,14 +38,6 @@
     ClassName(const ClassName&) = delete; \
     void operator=(const ClassName&) = delete;
 
-#if defined(_MSC_VER)
-namespace std {
-  inline bool isinf(double num) { return mozilla::IsInfinite(num); }
-  inline bool isnan(double num) { return mozilla::IsNaN(num); }
-  inline bool isfinite(double num) { return mozilla::IsFinite(num); }
-}
-#endif
-
 typedef std::string String;
 
 double mozToDouble(const String &aStr, bool *valid) {