diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index e829a88..392f84a 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -37,12 +37,10 @@ jobs:
 
       - uses: Swatinem/rust-cache@v2
 
-      - name: run tests with default features
-        run: cargo test --all
-      - name: run tests with embedded parser
-        run: cargo test --all --no-default-features
-      - name: run tests with generated parser
-        run: cargo test --all --all-features
+      - name: run tests with num-bigint
+        run: cargo test --all --no-default-features --features num-bigint
+      - name: run tests with malachite-bigint and all features
+        run: cargo test --all --features location,malachite-bigint,constant-optimization,fold,unparse,visitor,all-nodes-with-ranges,full-lexer,serde --exclude rustpython-ast-pyo3
 
   lint:
     name: Check Rust code with rustfmt and clippy
@@ -55,7 +53,9 @@ jobs:
       - name: run rustfmt
         run: cargo fmt --all -- --check
       - name: run clippy
-        run: cargo clippy --all --all-features -- -Dwarnings
+        run: cargo clippy --all --no-default-features --features num-bigint
+      - name: run clippy
+        run: cargo clippy --all --features location,malachite-bigint,constant-optimization,fold,unparse,visitor,all-nodes-with-ranges,full-lexer,serde --exclude rustpython-ast-pyo3 -- -Dwarnings
 
       - uses: actions/setup-python@v4
         with:
diff --git a/Cargo.toml b/Cargo.toml
index df2b843..2c8cbfc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,7 +21,7 @@ rustpython-ast = { path = "ast", default-features = false }
 rustpython-parser-core = { path = "core", features = [] }
 rustpython-literal = { path = "literal" }
 rustpython-format = { path = "format" }
-rustpython-parser = { path = "parser" }
+rustpython-parser = { path = "parser", default-features = false }
 
 ahash = "0.7.6"
 anyhow = "1.0.45"
@@ -34,6 +34,7 @@ num-complex = "0.4.0"
 num-bigint = "0.4.3"
 num-traits = "0.2"
 pyo3 = { version = "0.18.3" }
+malachite-bigint = { version = "0.1.0" }
 rand = "0.8.5"
 serde = "1.0"
 static_assertions = "1.1"
diff --git a/ast-pyo3/Cargo.toml b/ast-pyo3/Cargo.toml
index 80bddd3..bddf453 100644
--- a/ast-pyo3/Cargo.toml
+++ b/ast-pyo3/Cargo.toml
@@ -14,7 +14,7 @@ crate-type = ["cdylib"]
 
 [dependencies]
 rustpython-ast = { workspace = true, features = ["location"] }
-rustpython-parser = { workspace = true }
+rustpython-parser = { workspace = true, features = ["num-bigint"] }
 num-complex = { workspace = true }
 once_cell = { workspace = true }
 
diff --git a/ast/Cargo.toml b/ast/Cargo.toml
index cedfa50..d3229bc 100644
--- a/ast/Cargo.toml
+++ b/ast/Cargo.toml
@@ -8,7 +8,7 @@ repository = "https://github.com/RustPython/Parser/"
 license = "MIT"
 
 [features]
-default = ["location"]
+default = ["location", "malachite-bigint"]
 constant-optimization = ["fold"]
 location = ["fold", "rustpython-parser-core/location"]
 fold = []
@@ -21,7 +21,6 @@ rustpython-parser-core = { workspace = true }
 rustpython-literal = { workspace = true, optional = true }
 
 is-macro = { workspace = true }
-num-bigint = { workspace = true }
+num-bigint = { workspace = true, optional = true }
+malachite-bigint = { workspace = true, optional = true }
 static_assertions = "1.1.0"
-
-pyo3 = { workspace = true, optional = true, features = ["num-bigint", "num-complex"] }
diff --git a/ast/src/builtin.rs b/ast/src/builtin.rs
index 5811832..1a64efb 100644
--- a/ast/src/builtin.rs
+++ b/ast/src/builtin.rs
@@ -1,6 +1,6 @@
 //! `builtin_types` in asdl.py and Attributed
 
-use num_bigint::BigInt;
+use crate::bigint::BigInt;
 
 pub type String = std::string::String;
 
diff --git a/ast/src/lib.rs b/ast/src/lib.rs
index 94f5901..b55266c 100644
--- a/ast/src/lib.rs
+++ b/ast/src/lib.rs
@@ -14,6 +14,11 @@ mod ranged;
 #[cfg(feature = "unparse")]
 mod unparse;
 
+#[cfg(feature = "malachite-bigint")]
+pub use malachite_bigint as bigint;
+#[cfg(feature = "num-bigint")]
+pub use num_bigint as bigint;
+
 pub use builtin::*;
 pub use generic::*;
 pub use ranged::Ranged;
diff --git a/ast/src/optimizer.rs b/ast/src/optimizer.rs
index 9689163..42a6ddd 100644
--- a/ast/src/optimizer.rs
+++ b/ast/src/optimizer.rs
@@ -55,7 +55,7 @@ impl<U> crate::fold::Fold<U> for ConstantOptimizer {
 
 #[cfg(test)]
 mod tests {
-    use num_bigint::BigInt;
+    use crate::bigint::BigInt;
     use rustpython_parser_core::text_size::TextRange;
 
     #[cfg(feature = "constant-optimization")]
diff --git a/format/Cargo.toml b/format/Cargo.toml
index 931a730..7a9db25 100644
--- a/format/Cargo.toml
+++ b/format/Cargo.toml
@@ -12,5 +12,5 @@ rustpython-literal = { workspace = true }
 
 bitflags = "2.3.1"
 itertools = "0.10.5"
-num-bigint = { workspace = true }
+malachite-bigint = { workspace = true }
 num-traits = { workspace = true }
diff --git a/format/src/cformat.rs b/format/src/cformat.rs
index 77f1e1e..a207857 100644
--- a/format/src/cformat.rs
+++ b/format/src/cformat.rs
@@ -1,7 +1,7 @@
 //! Implementation of Printf-Style string formatting
 //! as per the [Python Docs](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting).
 use bitflags::bitflags;
-use num_bigint::{BigInt, Sign};
+use malachite_bigint::{BigInt, Sign};
 use num_traits::Signed;
 use rustpython_literal::{float, format::Case};
 use std::{
diff --git a/format/src/format.rs b/format/src/format.rs
index c10d37b..e2dff8b 100644
--- a/format/src/format.rs
+++ b/format/src/format.rs
@@ -1,5 +1,5 @@
 use itertools::{Itertools, PeekingNext};
-use num_bigint::{BigInt, Sign};
+use malachite_bigint::{BigInt, Sign};
 use num_traits::{cast::ToPrimitive, Signed};
 use rustpython_literal::float;
 use rustpython_literal::format::Case;
diff --git a/parser/Cargo.toml b/parser/Cargo.toml
index 824ce61..863a28a 100644
--- a/parser/Cargo.toml
+++ b/parser/Cargo.toml
@@ -9,11 +9,13 @@ license = "MIT"
 edition = "2021"
 
 [features]
-default = ["location"]
+default = ["location", "malachite-bigint"]
 location = ["rustpython-ast/location", "rustpython-parser-core/location"]
 serde = ["dep:serde", "rustpython-parser-core/serde"]
 all-nodes-with-ranges = ["rustpython-ast/all-nodes-with-ranges"]
 full-lexer = []
+malachite-bigint = ["dep:malachite-bigint", "rustpython-ast/malachite-bigint"]
+num-bigint = ["dep:num-bigint", "rustpython-ast/num-bigint"]
 
 [build-dependencies]
 anyhow = { workspace = true }
@@ -28,7 +30,8 @@ rustpython-parser-core = { workspace = true }
 itertools = { workspace = true }
 is-macro = { workspace = true }
 log = { workspace = true }
-num-bigint = { workspace = true }
+malachite-bigint = { workspace = true, optional = true }
+num-bigint = { workspace = true, optional = true }
 num-traits = { workspace = true }
 unicode_names2 = { workspace = true }
 
diff --git a/parser/src/lexer.rs b/parser/src/lexer.rs
index fac0dc0..862b8ae 100644
--- a/parser/src/lexer.rs
+++ b/parser/src/lexer.rs
@@ -28,6 +28,7 @@
 //!
 //! [Lexical analysis]: https://docs.python.org/3/reference/lexical_analysis.html
 use crate::{
+    ast::bigint::BigInt,
     soft_keywords::SoftKeywordTransformer,
     string::FStringErrorType,
     text_size::{TextLen, TextRange, TextSize},
@@ -35,7 +36,6 @@ use crate::{
     Mode,
 };
 use log::trace;
-use num_bigint::BigInt;
 use num_traits::{Num, Zero};
 use std::{char, cmp::Ordering, ops::Index, slice::SliceIndex, str::FromStr};
 use unic_emoji_char::is_emoji_presentation;
@@ -466,6 +466,13 @@ where
         }
     }
 
+    #[cfg(feature = "full-lexer")]
+    fn lex_and_emit_comment(&mut self) -> Result<(), LexicalError> {
+        let comment = self.lex_comment()?;
+        self.emit(comment);
+        Ok(())
+    }
+
     /// Discard comment if full-lexer is not enabled.
     #[cfg(not(feature = "full-lexer"))]
     fn lex_comment(&mut self) {
@@ -480,6 +487,13 @@ where
         }
     }
 
+    #[cfg(not(feature = "full-lexer"))]
+    #[inline]
+    fn lex_and_emit_comment(&mut self) -> Result<(), LexicalError> {
+        self.lex_comment();
+        Ok(())
+    }
+
     /// Lex a string literal.
     fn lex_string(&mut self, kind: StringKind) -> LexResult {
         let start_pos = self.get_pos();
@@ -626,9 +640,7 @@ where
                     tabs += 1;
                 }
                 Some('#') => {
-                    let _comment = self.lex_comment();
-                    #[cfg(feature = "full-lexer")]
-                    self.emit(_comment?);
+                    self.lex_and_emit_comment()?;
                     spaces = 0;
                     tabs = 0;
                 }
@@ -775,9 +787,7 @@ where
                 self.emit(number);
             }
             '#' => {
-                let _comment = self.lex_comment();
-                #[cfg(feature = "full-lexer")]
-                self.emit(_comment?);
+                self.lex_and_emit_comment()?;
             }
             '"' | '\'' => {
                 let string = self.lex_string(StringKind::String)?;
@@ -1360,7 +1370,7 @@ impl std::fmt::Display for LexicalErrorType {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use num_bigint::BigInt;
+    use crate::ast::bigint::BigInt;
 
     const WINDOWS_EOL: &str = "\r\n";
     const MAC_EOL: &str = "\r";
diff --git a/parser/src/parser.rs b/parser/src/parser.rs
index 4dd38d6..ba64343 100644
--- a/parser/src/parser.rs
+++ b/parser/src/parser.rs
@@ -284,7 +284,6 @@ pub fn parse_program(source: &str, source_path: &str) -> Result<ast::Suite, Pars
 /// For example, parsing a single expression denoting the addition of two numbers:
 ///
 ///  ```
-/// extern crate num_bigint;
 /// use rustpython_parser as parser;
 /// let expr = parser::parse_expression("1 + 2", "<embedded>");
 ///
diff --git a/parser/src/python.lalrpop b/parser/src/python.lalrpop
index aefe64a..31eefe7 100644
--- a/parser/src/python.lalrpop
+++ b/parser/src/python.lalrpop
@@ -4,7 +4,7 @@
 // See also: https://greentreesnakes.readthedocs.io/en/latest/nodes.html#keyword
 
 use crate::{
-    ast::{self as ast, Ranged},
+    ast::{self as ast, Ranged, bigint::BigInt},
     lexer::{LexicalError, LexicalErrorType},
     function::{ArgumentList, parse_args, validate_pos_params, validate_arguments},
     context::set_context,
@@ -12,7 +12,6 @@ use crate::{
     token::{self, StringKind},
     text_size::TextSize, parser::optional_range
 };
-use num_bigint::BigInt;
 
 grammar;
 
diff --git a/parser/src/python.rs b/parser/src/python.rs
index 66e3ba8..29e7922 100644
--- a/parser/src/python.rs
+++ b/parser/src/python.rs
@@ -1,7 +1,7 @@
 // auto-generated: "lalrpop 0.20.0"
-// sha3: 4ad71899432c2dd721d23812499e7f4385a10cb13467dbf34b4043443888f745
+// sha3: b94dbacf01253c4fc4605d489e98f5929504a78e0baa83381e126895ec61cb59
 use crate::{
-    ast::{self as ast, Ranged},
+    ast::{self as ast, Ranged, bigint::BigInt},
     lexer::{LexicalError, LexicalErrorType},
     function::{ArgumentList, parse_args, validate_pos_params, validate_arguments},
     context::set_context,
@@ -9,7 +9,6 @@ use crate::{
     token::{self, StringKind},
     text_size::TextSize, parser::optional_range
 };
-use num_bigint::BigInt;
 #[allow(unused_extern_crates)]
 extern crate lalrpop_util as __lalrpop_util;
 #[allow(unused_imports)]
@@ -22,7 +21,7 @@ extern crate alloc;
 mod __parse__Top {
 
     use crate::{
-    ast::{self as ast, Ranged},
+    ast::{self as ast, Ranged, bigint::BigInt},
     lexer::{LexicalError, LexicalErrorType},
     function::{ArgumentList, parse_args, validate_pos_params, validate_arguments},
     context::set_context,
@@ -30,7 +29,6 @@ mod __parse__Top {
     token::{self, StringKind},
     text_size::TextSize, parser::optional_range
 };
-    use num_bigint::BigInt;
     #[allow(unused_extern_crates)]
     extern crate lalrpop_util as __lalrpop_util;
     #[allow(unused_imports)]
diff --git a/parser/src/token.rs b/parser/src/token.rs
index e60d655..f472eeb 100644
--- a/parser/src/token.rs
+++ b/parser/src/token.rs
@@ -4,8 +4,8 @@
 //! loosely based on the token definitions found in the [CPython source].
 //!
 //! [CPython source]: https://github.com/python/cpython/blob/dfc2e065a2e71011017077e549cd2f9bf4944c54/Include/internal/pycore_token.h
+use crate::ast::bigint::BigInt;
 use crate::{text_size::TextSize, Mode};
-use num_bigint::BigInt;
 use std::fmt;
 
 /// The set of tokens the Python source code can be tokenized in.