diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5c2cb9fdd..82bc4a9d4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,7 +46,9 @@ jobs:
           - { os: ubuntu-22.04,   rust-version: stable,  target: 'x86_64-unknown-linux-gnu', publish: true }
           - { os: ubuntu-22.04,   rust-version: stable,  target: 'i686-unknown-linux-gnu',   publish: true }
           # FIXME(issue #2138): run wasm tests, failing to run since https://github.com/mthom/scryer-prolog/pull/2137 removed wasm-pack
-          - { os: ubuntu-22.04,   rust-version: nightly, target: 'wasm32-unknown-unknown',   publish: true, args: '--no-default-features' , test-args: '--no-run --no-default-features' }
+          - { os: ubuntu-22.04,   rust-version: nightly, target: 'wasm32-unknown-unknown',   publish: true, args: '--no-default-features' , test-args: '--no-run --no-default-features', use_swap: true }
+          # Cargo.toml rust-version
+          - { os: ubuntu-22.04,   rust-version: "1.77",  target: 'x86_64-unknown-linux-gnu'}
           # rust versions
           - { os: ubuntu-22.04,   rust-version: beta,    target: 'x86_64-unknown-linux-gnu'}
           - { os: ubuntu-22.04,   rust-version: nightly, target: 'x86_64-unknown-linux-gnu'}
@@ -55,6 +57,10 @@ jobs:
         shell: bash
     steps:
       - uses: actions/checkout@v4
+      - uses: actionhippie/swap-space@v1
+        if: matrix.use_swap
+        with:
+          size: 10G
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
diff --git a/src/machine/machine_indices.rs b/src/machine/machine_indices.rs
index 830cc91f2..856c7766b 100644
--- a/src/machine/machine_indices.rs
+++ b/src/machine/machine_indices.rs
@@ -18,8 +18,6 @@ use std::collections::BTreeSet;
 use std::ops::{Deref, DerefMut};
 
 use crate::types::*;
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub(crate) struct OrderedOpDirKey(pub(crate) Atom, pub(crate) Fixity);
 
 // 7.2
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
diff --git a/src/machine/streams.rs b/src/machine/streams.rs
index c2adb47e3..be5591cf1 100644
--- a/src/machine/streams.rs
+++ b/src/machine/streams.rs
@@ -24,7 +24,6 @@ use std::io;
 #[cfg(feature = "http")]
 use std::io::BufRead;
 use std::io::{Cursor, ErrorKind, Read, Seek, SeekFrom, Write};
-use std::mem;
 use std::net::{Shutdown, TcpStream};
 use std::ops::{Deref, DerefMut};
 use std::path::PathBuf;
@@ -296,9 +295,9 @@ impl Read for HttpReadStream {
 #[cfg(feature = "http")]
 pub struct HttpWriteStream {
     status_code: u16,
-    headers: mem::ManuallyDrop<hyper::HeaderMap>,
+    headers: std::mem::ManuallyDrop<hyper::HeaderMap>,
     response: TypedArenaPtr<HttpResponse>,
-    buffer: mem::ManuallyDrop<Vec<u8>>,
+    buffer: std::mem::ManuallyDrop<Vec<u8>>,
 }
 
 #[cfg(feature = "http")]
@@ -325,8 +324,8 @@ impl Write for HttpWriteStream {
 #[cfg(feature = "http")]
 impl HttpWriteStream {
     fn drop(&mut self) {
-        let headers = unsafe { mem::ManuallyDrop::take(&mut self.headers) };
-        let buffer = unsafe { mem::ManuallyDrop::take(&mut self.buffer) };
+        let headers = unsafe { std::mem::ManuallyDrop::take(&mut self.headers) };
+        let buffer = unsafe { std::mem::ManuallyDrop::take(&mut self.buffer) };
 
         let (ready, response, cvar) = &**self.response;
 
@@ -1228,8 +1227,8 @@ impl Stream {
             StreamLayout::new(CharReader::new(HttpWriteStream {
                 response,
                 status_code,
-                headers: mem::ManuallyDrop::new(headers),
-                buffer: mem::ManuallyDrop::new(Vec::new()),
+                headers: std::mem::ManuallyDrop::new(headers),
+                buffer: std::mem::ManuallyDrop::new(Vec::new()),
             })),
             arena
         ))
diff --git a/src/machine/unify.rs b/src/machine/unify.rs
index b045552b8..7cd3df06f 100644
--- a/src/machine/unify.rs
+++ b/src/machine/unify.rs
@@ -453,30 +453,6 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         }
     }
 
-    fn unify_big_num<N>(&mut self, n1: TypedArenaPtr<N>, value: HeapCellValue)
-    where
-        N: PartialEq<Rational> + PartialEq<Integer> + PartialEq<i64> + ArenaAllocated,
-    {
-        if let Some(r) = value.as_var() {
-            Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
-            return;
-        }
-
-        match Number::try_from(value) {
-            Ok(n2) => match n2 {
-                Number::Fixnum(n2) if *n1 == n2.get_num() => {}
-                Number::Integer(n2) if *n1 == *n2 => {}
-                Number::Rational(n2) if *n1 == *n2 => {}
-                _ => {
-                    self.fail = true;
-                }
-            },
-            Err(_) => {
-                self.fail = true;
-            }
-        }
-    }
-
     fn unify_big_integer(&mut self, n1: TypedArenaPtr<Integer>, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
             Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
diff --git a/src/parser/parser.rs b/src/parser/parser.rs
index 47e829219..c4d509b4e 100644
--- a/src/parser/parser.rs
+++ b/src/parser/parser.rs
@@ -109,7 +109,7 @@ pub(crate) fn as_partial_string(
                 tail_ref = succ;
             }
             Term::PartialString(_, pstr, tail) => {
-                string += &pstr;
+                string += pstr;
                 tail_ref = tail;
             }
             Term::CompleteString(_, cstr) => {