diff --git a/Cargo.toml b/Cargo.toml
index 7b6f9e1ce..08342a929 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -61,18 +61,20 @@ exclude = [
 [dev-dependencies]
 no-panic = "0.1.33"
 
-[profile.release]
-# Options for no-panic to correctly detect the lack of panics
-codegen-units = 1
-lto = "fat"
+# The default release profile is unchanged.
 
 # Release mode with debug assertions
 [profile.release-checked]
-codegen-units = 1
+inherits = "release"
 debug-assertions = true
+overflow-checks = true
+
+# Release with maximum optimizations, which is very slow to build. This is also
+# what is needed to check `no-panic`.
+[profile.release-opt]
 inherits = "release"
+codegen-units = 1
 lto = "fat"
-overflow-checks = true
 
 [profile.bench]
 # Required for iai-callgrind
diff --git a/build.rs b/build.rs
index ca4a639a1..7042b54d7 100644
--- a/build.rs
+++ b/build.rs
@@ -8,18 +8,9 @@ fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rustc-check-cfg=cfg(assert_no_panic)");
 
-    println!("cargo:rustc-check-cfg=cfg(feature, values(\"checked\"))");
-
-    #[allow(unexpected_cfgs)]
-    if !cfg!(feature = "checked") {
-        let lvl = env::var("OPT_LEVEL").unwrap();
-        if lvl != "0" && !cfg!(debug_assertions) {
-            println!("cargo:rustc-cfg=assert_no_panic");
-        } else if env::var("ENSURE_NO_PANIC").is_ok() {
-            // Give us a defensive way of ensureing that no-panic is checked  when we
-            // expect it to be.
-            panic!("`assert_no_panic `was not enabled");
-        }
+    // If set, enable `no-panic`. Requires LTO (`release-opt` profile).
+    if env::var("ENSURE_NO_PANIC").is_ok() {
+        println!("cargo:rustc-cfg=assert_no_panic");
     }
 
     configure::emit_libm_config(&cfg);
diff --git a/ci/run.sh b/ci/run.sh
index 296986d97..a946d325e 100755
--- a/ci/run.sh
+++ b/ci/run.sh
@@ -117,4 +117,14 @@ $cmd "$profile" release-checked --features unstable-intrinsics
 $cmd "$profile" release-checked --features unstable-intrinsics --benches
 
 # Ensure that the routines do not panic.
-ENSURE_NO_PANIC=1 cargo build -p libm --target "$target" --no-default-features --release
+# 
+# `--tests` must be passed because no-panic is only enabled as a dev
+# dependency. The `release-opt` profile must be used to enable LTO and a
+# single CGU.
+ENSURE_NO_PANIC=1 cargo build \
+     -p libm \
+    --target "$target" \
+    --no-default-features \
+    --features unstable-float \
+    --tests \
+    --profile release-opt
diff --git a/crates/compiler-builtins-smoke-test/Cargo.toml b/crates/compiler-builtins-smoke-test/Cargo.toml
index d578b0dcd..24b33645e 100644
--- a/crates/compiler-builtins-smoke-test/Cargo.toml
+++ b/crates/compiler-builtins-smoke-test/Cargo.toml
@@ -22,7 +22,6 @@ unexpected_cfgs = { level = "warn", check-cfg = [
   "cfg(arch_enabled)",
   "cfg(assert_no_panic)",
   "cfg(intrinsics_enabled)",
-  'cfg(feature, values("checked"))',
   'cfg(feature, values("force-soft-floats"))',
   'cfg(feature, values("unstable"))',
   'cfg(feature, values("unstable-intrinsics"))',
diff --git a/src/math/atan2.rs b/src/math/atan2.rs
index b9bf0da93..c668731cf 100644
--- a/src/math/atan2.rs
+++ b/src/math/atan2.rs
@@ -114,12 +114,18 @@ pub fn atan2(y: f64, x: f64) -> f64 {
     }
 }
 
-#[test]
-fn sanity_check() {
-    assert_eq!(atan2(0.0, 1.0), 0.0);
-    assert_eq!(atan2(0.0, -1.0), PI);
-    assert_eq!(atan2(-0.0, -1.0), -PI);
-    assert_eq!(atan2(3.0, 2.0), atan(3.0 / 2.0));
-    assert_eq!(atan2(2.0, -1.0), atan(2.0 / -1.0) + PI);
-    assert_eq!(atan2(-2.0, -1.0), atan(-2.0 / -1.0) - PI);
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg_attr(x86_no_sse, ignore = "FIXME(i586): possible incorrect rounding")]
+    fn sanity_check() {
+        assert_eq!(atan2(0.0, 1.0), 0.0);
+        assert_eq!(atan2(0.0, -1.0), PI);
+        assert_eq!(atan2(-0.0, -1.0), -PI);
+        assert_eq!(atan2(3.0, 2.0), atan(3.0 / 2.0));
+        assert_eq!(atan2(2.0, -1.0), atan(2.0 / -1.0) + PI);
+        assert_eq!(atan2(-2.0, -1.0), atan(-2.0 / -1.0) - PI);
+    }
 }
diff --git a/src/math/rem_pio2_large.rs b/src/math/rem_pio2_large.rs
index ec8397f4b..6d679bbe9 100644
--- a/src/math/rem_pio2_large.rs
+++ b/src/math/rem_pio2_large.rs
@@ -226,8 +226,9 @@ pub(crate) fn rem_pio2_large(x: &[f64], y: &mut [f64], e0: i32, prec: usize) ->
     let x1p24 = f64::from_bits(0x4170000000000000); // 0x1p24 === 2 ^ 24
     let x1p_24 = f64::from_bits(0x3e70000000000000); // 0x1p_24 === 2 ^ (-24)
 
-    #[cfg(all(target_pointer_width = "64", feature = "checked"))]
-    assert!(e0 <= 16360);
+    if cfg!(target_pointer_width = "64") {
+        debug_assert!(e0 <= 16360);
+    }
 
     let nx = x.len();
 
diff --git a/src/math/sin.rs b/src/math/sin.rs
index e04e0d6a0..229fa4bef 100644
--- a/src/math/sin.rs
+++ b/src/math/sin.rs
@@ -81,12 +81,15 @@ pub fn sin(x: f64) -> f64 {
     }
 }
 
-#[test]
-fn test_near_pi() {
-    let x = f64::from_bits(0x400921fb000FD5DD); // 3.141592026217707
-    let sx = f64::from_bits(0x3ea50d15ced1a4a2); // 6.273720864039205e-7
-    let result = sin(x);
-    #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-    let result = force_eval!(result);
-    assert_eq!(result, sx);
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg_attr(x86_no_sse, ignore = "FIXME(i586): possible incorrect rounding")]
+    fn test_near_pi() {
+        let x = f64::from_bits(0x400921fb000FD5DD); // 3.141592026217707
+        let sx = f64::from_bits(0x3ea50d15ced1a4a2); // 6.273720864039205e-7
+        assert_eq!(sin(x), sx);
+    }
 }