diff --git a/src/racket/src/number.c b/src/racket/src/number.c
index d8589de568..a1b7cf4b80 100644
--- a/src/racket/src/number.c
+++ b/src/racket/src/number.c
@@ -2735,7 +2735,7 @@ double scheme_double_expt(double x, double y) {
     return not_a_number_val;
   else if ((x == 0.0) && (y <= 0))
     return not_a_number_val;
-  else if (isnan(x) || isnan(y))
+  else if (MZ_IS_NAN(x) || MZ_IS_NAN(y))
     return not_a_number_val;
   else
     return sch_pow(x, y);