diff --git a/internal/ceres/rotation_test.cc b/internal/ceres/rotation_test.cc
index a8351d5..55a4fbb 100644
--- a/internal/ceres/rotation_test.cc
+++ b/internal/ceres/rotation_test.cc
@@ -591,8 +591,8 @@
 
 
 bool IsClose(double x, double y) {
-  EXPECT_FALSE(isnan(x));
-  EXPECT_FALSE(isnan(y));
+  EXPECT_FALSE(IsNaN(x));
+  EXPECT_FALSE(IsNaN(y));
   double absdiff = fabs(x - y);
   if (x == 0 || y == 0) {
     return absdiff <= kTolerance;