diff --git a/CMakeLists.txt b/CMakeLists.txt
index 328dfdd0..61824342 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -232,6 +232,11 @@ check_cxx_source_compiles(
     void f() { isnan(0.0);} "
     HAVE_ISNAN)
 
+check_cxx_source_compiles(
+    "#include <cmath> 
+    void f() { std::isnan(0.0);} "
+    HAVE_STD_ISNAN)
+
 if(CMAKE_COMPILER_IS_GNUCXX)
     set(WARNING_FLAGS_CXX "-Wall")
     set(WARNING_FLAGS_C   "-Wall")
diff --git a/simgear/math/SGGeod.hxx b/simgear/math/SGGeod.hxx
index 2ab2b107..8eddbe92 100644
--- a/simgear/math/SGGeod.hxx
+++ b/simgear/math/SGGeod.hxx
@@ -20,10 +20,6 @@
 
 #include <simgear/constants.h>
 
-#ifndef _MSC_VER
-using std::isnan;
-#endif
-
 // #define SG_GEOD_NATIVE_DEGREE
 
 /// Class representing a geodetic location
@@ -356,7 +352,10 @@ inline
 bool
 SGGeod::isValid() const
 {
-  if (isnan(_lon) || isnan(_lat)) return false;
+  if (SGMiscd::isNaN(_lon))
+      return false;
+  if (SGMiscd::isNaN(_lat))
+      return false;
 #ifdef SG_GEOD_NATIVE_DEGREE
   return (_lon >= -180.0) && (_lon <= 180.0) &&
   (_lat >= -90.0) && (_lat <= 90.0);
diff --git a/simgear/math/SGMisc.hxx b/simgear/math/SGMisc.hxx
index 5e69077e..8eaa124e 100644
--- a/simgear/math/SGMisc.hxx
+++ b/simgear/math/SGMisc.hxx
@@ -92,7 +92,6 @@ public:
   static S lerp(const S& val0, const S& val1, const T& t)
   { return val0*(T(1) - t) + val1*t; }
 
-#ifndef NDEBUG
   /// Returns true if v is a NaN value
   /// Use with care: allways code that you do not need to use that!
   static bool isNaN(const T& v)
@@ -109,7 +108,6 @@ public:
     return !(v == v);
 #endif
   }
-#endif
 };
 
 #endif
diff --git a/simgear/simgear_config_cmake.h.in b/simgear/simgear_config_cmake.h.in
index a9d12392..c571af2d 100644
--- a/simgear/simgear_config_cmake.h.in
+++ b/simgear/simgear_config_cmake.h.in
@@ -10,6 +10,7 @@
 #cmakedefine HAVE_RINT
 #cmakedefine HAVE_TIMEGM
 #cmakedefine HAVE_ISNAN
+#cmakedefine HAVE_STD_ISNAN
 #cmakedefine HAVE_WINDOWS_H
 #cmakedefine HAVE_MKDTEMP