diff --git a/build.rs b/build.rs
index 490b6391..b520b624 100644
--- a/build.rs
+++ b/build.rs
@@ -8,6 +8,9 @@ fn main() {
 
     println!("cargo:compiler-rt={}", cwd.join("compiler-rt").display());
 
+    // Activate libm's unstable features to make full use of Nightly.
+    println!("cargo:rustc-cfg=feature=\"unstable\"");
+
     // Emscripten's runtime includes all the builtins
     if target.contains("emscripten") {
         return;
diff --git a/libm b/libm
index 01bee72a..8eedc247 160000
--- a/libm
+++ b/libm
@@ -1 +1 @@
-Subproject commit 01bee72a93ebaeea2883d0f963174c2b00d4fe68
+Subproject commit 8eedc2470531f51b978e4c873ee78a33c90e0fbd