diff --git a/library/core/src/convert/num.rs b/library/core/src/convert/num.rs
index c69026c5c9f3..75c94af30000 100644
--- a/library/core/src/convert/num.rs
+++ b/library/core/src/convert/num.rs
@@ -39,62 +39,51 @@ impl_float_to_int!(f32 => u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i12
 impl_float_to_int!(f64 => u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
 impl_float_to_int!(f128 => u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
 
-// Conversion traits for primitive integer and float types
-// Conversions T -> T are covered by a blanket impl and therefore excluded
-// Some conversions from and to usize/isize are not implemented due to portability concerns
-macro_rules! impl_from {
-    (bool => $Int:ty $(,)?) => {
-        impl_from!(
-            bool => $Int,
-            #[stable(feature = "from_bool", since = "1.28.0")],
-            concat!(
-                "Converts a [`bool`] to [`", stringify!($Int), "`] losslessly.\n",
-                "The resulting value is `0` for `false` and `1` for `true` values.\n",
-                "\n",
-                "# Examples\n",
-                "\n",
-                "```\n",
-                "assert_eq!(", stringify!($Int), "::from(true), 1);\n",
-                "assert_eq!(", stringify!($Int), "::from(false), 0);\n",
-                "```\n",
-            ),
-        );
-    };
-    ($Small:ty => $Large:ty, #[$attr:meta] $(,)?) => {
-        impl_from!(
-            $Small => $Large,
-            #[$attr],
-            concat!("Converts [`", stringify!($Small), "`] to [`", stringify!($Large), "`] losslessly."),
-        );
-    };
-    ($Small:ty => $Large:ty, #[$attr:meta], $doc:expr $(,)?) => {
-        #[$attr]
+/// Implement `From<bool>` for integers
+macro_rules! impl_from_bool {
+    ($($int:ty)*) => {$(
+        #[stable(feature = "from_bool", since = "1.28.0")]
         #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
-        impl const From<$Small> for $Large {
-            // Rustdocs on the impl block show a "[+] show undocumented items" toggle.
-            // Rustdocs on functions do not.
-            #[doc = $doc]
+        impl const From<bool> for $int {
+            /// Converts from [`bool`] to
+            #[doc = concat!("[`", stringify!($int), "`]")]
+            /// , by turning `false` into `0` and `true` into `1`.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            #[doc = concat!("assert_eq!(", stringify!($int), "::from(false), 0);")]
+            ///
+            #[doc = concat!("assert_eq!(", stringify!($int), "::from(true), 1);")]
+            /// ```
             #[inline(always)]
-            fn from(small: $Small) -> Self {
-                small as Self
+            fn from(b: bool) -> Self {
+                b as Self
             }
         }
-    };
+    )*}
 }
 
 // boolean -> integer
-impl_from!(bool => u8);
-impl_from!(bool => u16);
-impl_from!(bool => u32);
-impl_from!(bool => u64);
-impl_from!(bool => u128);
-impl_from!(bool => usize);
-impl_from!(bool => i8);
-impl_from!(bool => i16);
-impl_from!(bool => i32);
-impl_from!(bool => i64);
-impl_from!(bool => i128);
-impl_from!(bool => isize);
+impl_from_bool!(u8 u16 u32 u64 u128 usize);
+impl_from_bool!(i8 i16 i32 i64 i128 isize);
+
+/// Implement `From<$small>` for `$large`
+macro_rules! impl_from {
+    ($small:ty => $large:ty, #[$attr:meta]) => {
+        #[$attr]
+        #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
+        impl const From<$small> for $large {
+            #[doc = concat!("Converts from [`", stringify!($small), "`] to [`", stringify!($large), "`] losslessly.")]
+            #[inline(always)]
+            fn from(small: $small) -> Self {
+                debug_assert!(<$large>::MIN as i128 <= <$small>::MIN as i128);
+                debug_assert!(<$small>::MAX as u128 <= <$large>::MAX as u128);
+                small as Self
+            }
+        }
+    }
+}
 
 // unsigned integer -> unsigned integer
 impl_from!(u8 => u16, #[stable(feature = "lossless_int_conv", since = "1.5.0")]);