diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index d25e569bc..0e005b735 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -220,8 +220,8 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
             profile: minimal
-            toolchain: stable
-            components: rustfmt
+            toolchain: nightly
+            components: rustfmt, clippy
             override: true
       - name: run rustfmt
         uses: actions-rs/cargo@v1
diff --git a/stdlib/src/zlib.rs b/stdlib/src/zlib.rs
index 7d861a7e9..330ddc89e 100644
--- a/stdlib/src/zlib.rs
+++ b/stdlib/src/zlib.rs
@@ -154,7 +154,7 @@ mod zlib {
     fn header_from_wbits(wbits: OptionalArg<i8>, vm: &VirtualMachine) -> PyResult<InitOptions> {
         let wbits = wbits.unwrap_or(MAX_WBITS as i8);
         let header = wbits > 0;
-        let wbits = wbits.abs() as u8;
+        let wbits = wbits.unsigned_abs();
         match wbits {
             9..=15 => Ok(InitOptions::Standard {
                 header,
diff --git a/vm/src/cformat.rs b/vm/src/cformat.rs
index 7e1267f77..09f7dd979 100644
--- a/vm/src/cformat.rs
+++ b/vm/src/cformat.rs
@@ -599,8 +599,8 @@ fn try_update_quantity_from_tuple<'a, I: Iterator<Item = &'a PyObjectRef>>(
         Some(CFormatQuantity::FromValuesTuple) => match elements.next() {
             Some(width_obj) => {
                 if let Some(i) = width_obj.payload::<PyInt>() {
-                    let i = i.try_to_primitive::<i32>(vm)?.abs() as usize;
-                    *q = Some(CFormatQuantity::Amount(i));
+                    let i = i.try_to_primitive::<i32>(vm)?.unsigned_abs();
+                    *q = Some(CFormatQuantity::Amount(i as usize));
                     Ok(())
                 } else {
                     Err(vm.new_type_error("* wants int".to_owned()))
@@ -953,7 +953,7 @@ where
                     break;
                 }
             }
-            return Ok(Some(CFormatQuantity::Amount(num.abs() as usize)));
+            return Ok(Some(CFormatQuantity::Amount(num.unsigned_abs() as usize)));
         }
     }
     Ok(None)