diff --git a/src/libCom/osi/os/vxWorks/isnan.c b/src/libCom/osi/os/vxWorks/isnan.c
new file mode 100644
index 000000000..56f049181
--- /dev/null
+++ b/src/libCom/osi/os/vxWorks/isnan.c
@@ -0,0 +1,8 @@
+int isnan(double d)
+{
+        union { long l[2]; double d; } u;
+        u.d = d;
+        if ((u.l[0] & 0x7ff00000) != 0x7ff00000) return(0);
+        if (u.l[1] || (u.l[0] & 0x000fffff)) return(1);
+        return(0);
+}