diff --git a/tests/d2s_test.rs b/tests/d2s_test.rs
index 368cab6..7e8eba6 100644
--- a/tests/d2s_test.rs
+++ b/tests/d2s_test.rs
@@ -82,7 +82,8 @@ fn test_basic() {
     check!(-0.0);
     check!(1.0);
     check!(-1.0);
-    assert_eq!(pretty(f64::NAN), "NaN");
+    assert_eq!(pretty(f64::NAN.copysign(1.0)), "NaN");
+    assert_eq!(pretty(f64::NAN.copysign(-1.0)), "NaN");
     assert_eq!(pretty(f64::INFINITY), "inf");
     assert_eq!(pretty(f64::NEG_INFINITY), "-inf");
 }
diff --git a/tests/f2s_test.rs b/tests/f2s_test.rs
index 927fa7e..d6249a3 100644
--- a/tests/f2s_test.rs
+++ b/tests/f2s_test.rs
@@ -75,7 +75,8 @@ fn test_basic() {
     check!(-0.0);
     check!(1.0);
     check!(-1.0);
-    assert_eq!(pretty(f32::NAN), "NaN");
+    assert_eq!(pretty(f32::NAN.copysign(1.0)), "NaN");
+    assert_eq!(pretty(f32::NAN.copysign(-1.0)), "NaN");
     assert_eq!(pretty(f32::INFINITY), "inf");
     assert_eq!(pretty(f32::NEG_INFINITY), "-inf");
 }