diff --git a/glib/gdatetime.c b/glib/gdatetime.c
index 02cc3bd01..a43efab0b 100644
--- a/glib/gdatetime.c
+++ b/glib/gdatetime.c
@@ -80,6 +80,11 @@
 #ifndef G_OS_WIN32
 #include <sys/time.h>
 #include <time.h>
+#else
+#if defined (_MSC_VER) && (_MSC_VER < 1800)
+/* fallback implementation for isnan() on VS2012 and earlier */
+#define isnan _isnan
+#endif
 #endif /* !G_OS_WIN32 */
 
 /**
diff --git a/glib/tests/gdatetime.c b/glib/tests/gdatetime.c
index 0203dd0c2..3b1d9cf7d 100644
--- a/glib/tests/gdatetime.c
+++ b/glib/tests/gdatetime.c
@@ -29,6 +29,10 @@
 #ifdef G_OS_WIN32
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
+
+#ifndef NAN
+#define NAN HUGE_VAL * 0.0f
+#endif
 #endif
 
 #define ASSERT_DATE(dt,y,m,d) G_STMT_START { \