diff --git a/src/lib.rs b/src/lib.rs
index a47883d8..81b76f87 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -73,8 +73,7 @@ pub trait F32Ext: private::Sealed + Sized {
 
     fn abs(self) -> Self;
 
-    // NOTE depends on unstable intrinsics::copysignf32
-    // fn signum(self) -> Self;
+    fn signum(self) -> Self;
 
     fn mul_add(self, a: Self, b: Self) -> Self;
 
@@ -178,6 +177,15 @@ impl F32Ext for f32 {
         fabsf(self)
     }
 
+    #[inline]
+    fn signum(self) -> Self {
+        if self.is_nan() {
+            f32::NAN
+        } else {
+            copysignf(1., self)
+        }
+    }
+
     #[inline]
     fn mul_add(self, a: Self, b: Self) -> Self {
         fmaf(self, a, b)
@@ -361,8 +369,7 @@ pub trait F64Ext: private::Sealed + Sized {
 
     fn abs(self) -> Self;
 
-    // NOTE depends on unstable intrinsics::copysignf64
-    // fn signum(self) -> Self;
+    fn signum(self) -> Self;
 
     fn mul_add(self, a: Self, b: Self) -> Self;
 
@@ -466,6 +473,15 @@ impl F64Ext for f64 {
         fabs(self)
     }
 
+    #[inline]
+    fn signum(self) -> Self {
+        if self.is_nan() {
+            f64::NAN
+        } else {
+            copysign(1., self)
+        }
+    }
+
     #[inline]
     fn mul_add(self, a: Self, b: Self) -> Self {
         fma(self, a, b)