diff --git a/lang/cem/libcc.ansi/math/isnan.c b/lang/cem/libcc.ansi/math/isnan.c
new file mode 100644
index 000000000..21497a9cd
--- /dev/null
+++ b/lang/cem/libcc.ansi/math/isnan.c
@@ -0,0 +1,11 @@
+__IsNan(double d)
+{
+#if defined(vax) || defined(pdp)
+#else
+	float f = d;
+
+	if ((*((long *) &f) & 0x7f800000) == 0x7f800000 &&
+	    (*((long *) &f) & 0x007fffff) != 0) return 1;
+#endif
+	return 0;
+}