diff --git a/uppsrc/Core/Defs.h b/uppsrc/Core/Defs.h
index 72cff59ee..c2b6f7984 100644
--- a/uppsrc/Core/Defs.h
+++ b/uppsrc/Core/Defs.h
@@ -330,14 +330,22 @@ typedef long long unsigned uint64;
 typedef uint64             qword;
 
 #ifdef PLATFORM_WIN32
-inline bool IsNaN(double d) { return findarg(_fpclass(d), _FPCLASS_QNAN, _FPCLASS_SNAN) >= 0; }
-inline bool IsInf(double d) { return findarg(_fpclass(d), _FPCLASS_PINF, _FPCLASS_NINF) >= 0; }
+#ifdef COMPILER_MINGW
+inline bool IsNaN(double d)        { return std::isnan(d); }
+inline bool IsInf(double d)        { return std::isinf(d); }
 #else
-inline bool IsNaN(double d) { return fpclassify(d) == FP_NAN; }
-inline bool IsInf(double d) { return fpclassify(d) == FP_INFINITY; }
+inline bool IsNaN(double d)        { return _isnan(d); }
+inline bool IsInf(double d)        { return _finite(d) && !_isnan(d); }
+#endif
+#elif __APPLE__
+inline bool IsNaN(double d)        { return std::isnan(d); }
+inline bool IsInf(double d)        { return std::isinf(d); }
+#else
+inline bool IsNaN(double d)        { return isnan(d); }
+inline bool IsInf(double d)        { return isinf(d); }
 #endif
 
-inline bool IsFin(double d) { return !IsNaN(d) && !IsInf(d); }
+inline bool IsFin(double d)        { return !IsNaN(d) && !IsInf(d); }
 
 #ifdef COMPILER_MSC
 	#define I64(c) ((int64)COMBINE(c, i64))
diff --git a/uppsrc/Core/OL_Set.cpp b/uppsrc/Core/OL_Set.cpp
index bf768b166..315c077c3 100644
--- a/uppsrc/Core/OL_Set.cpp
+++ b/uppsrc/Core/OL_Set.cpp
@@ -1,5 +1,7 @@
 //#BLITZ_PROHIBIT
 
+// This file is explicitly removed from BLITZ to avoid inline optimizations
+
 #ifndef flagNONAMESPACE
 namespace Upp {
 #endif