diff --git a/CHANGELOG.md b/CHANGELOG.md
index f267740..e7aded5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Unreleased
+
+- Bump MSRV to 1.83.
+- Update `pyo3` to 0.28.
+
 ## 0.27.0 - 2025-11-07
 - Update to PyO3 0.27
 
diff --git a/Cargo.toml b/Cargo.toml
index 4a714a3..641b199 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,7 +3,7 @@ name = "pythonize"
 version = "0.27.0"
 authors = ["David Hewitt <1939362+davidhewitt@users.noreply.github.com>"]
 edition = "2021"
-rust-version = "1.74"
+rust-version = "1.83"
 license = "MIT"
 description = "Serde Serializer & Deserializer from Rust <--> Python, backed by PyO3."
 homepage = "https://github.com/davidhewitt/pythonize"
@@ -13,11 +13,11 @@ documentation = "https://docs.rs/crate/pythonize/"
 
 [dependencies]
 serde = { version = "1.0", default-features = false, features = ["std"] }
-pyo3 = { version = "0.27", default-features = false }
+pyo3 = { version = "0.28", default-features = false }
 
 [dev-dependencies]
 serde = { version = "1.0", default-features = false, features = ["derive"] }
-pyo3 = { version = "0.27", default-features = false, features = ["auto-initialize", "macros", "py-clone"] }
+pyo3 = { version = "0.28", default-features = false, features = ["auto-initialize", "macros", "py-clone"] }
 serde_json = "1.0"
 serde_bytes = "0.11"
 maplit = "1.0.2"
diff --git a/src/de.rs b/src/de.rs
index a30dbca..8b487db 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -520,7 +520,6 @@ mod test {
     use super::*;
     use crate::error::ErrorImpl;
     use maplit::hashmap;
-    use pyo3::ffi::c_str;
     use pyo3::{IntoPyObject, Python};
     use serde_json::{json, Value as JsonValue};
 
@@ -545,7 +544,7 @@ mod test {
 
         let expected = Empty;
         let expected_json = json!(null);
-        let code = c_str!("None");
+        let code = c"None";
         test_de(code, &expected, &expected_json);
     }
 
@@ -571,7 +570,7 @@ mod test {
             "baz": 45.23,
             "qux": true
         });
-        let code = c_str!("{'foo': 'Foo', 'bar': 8, 'baz': 45.23, 'qux': True}");
+        let code = c"{'foo': 'Foo', 'bar': 8, 'baz': 45.23, 'qux': True}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -583,7 +582,7 @@ mod test {
             bar: usize,
         }
 
-        let code = c_str!("{'foo': 'Foo'}");
+        let code = c"{'foo': 'Foo'}";
 
         Python::attach(|py| {
             let locals = PyDict::new(py);
@@ -602,7 +601,7 @@ mod test {
 
         let expected = TupleStruct("cat".to_string(), -10.05);
         let expected_json = json!(["cat", -10.05]);
-        let code = c_str!("('cat', -10.05)");
+        let code = c"('cat', -10.05)";
         test_de(code, &expected, &expected_json);
     }
 
@@ -611,7 +610,7 @@ mod test {
         #[derive(Debug, Deserialize, PartialEq)]
         struct TupleStruct(String, f64);
 
-        let code = c_str!("('cat', -10.05, 'foo')");
+        let code = c"('cat', -10.05, 'foo')";
 
         Python::attach(|py| {
             let locals = PyDict::new(py);
@@ -630,7 +629,7 @@ mod test {
 
         let expected = TupleStruct("cat".to_string(), -10.05);
         let expected_json = json!(["cat", -10.05]);
-        let code = c_str!("['cat', -10.05]");
+        let code = c"['cat', -10.05]";
         test_de(code, &expected, &expected_json);
     }
 
@@ -638,7 +637,7 @@ mod test {
     fn test_tuple() {
         let expected = ("foo".to_string(), 5);
         let expected_json = json!(["foo", 5]);
-        let code = c_str!("('foo', 5)");
+        let code = c"('foo', 5)";
         test_de(code, &expected, &expected_json);
     }
 
@@ -646,7 +645,7 @@ mod test {
     fn test_tuple_from_pylist() {
         let expected = ("foo".to_string(), 5);
         let expected_json = json!(["foo", 5]);
-        let code = c_str!("['foo', 5]");
+        let code = c"['foo', 5]";
         test_de(code, &expected, &expected_json);
     }
 
@@ -654,7 +653,7 @@ mod test {
     fn test_vec_from_pyset() {
         let expected = vec!["foo".to_string()];
         let expected_json = json!(["foo"]);
-        let code = c_str!("{'foo'}");
+        let code = c"{'foo'}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -662,7 +661,7 @@ mod test {
     fn test_vec_from_pyfrozenset() {
         let expected = vec!["foo".to_string()];
         let expected_json = json!(["foo"]);
-        let code = c_str!("frozenset({'foo'})");
+        let code = c"frozenset({'foo'})";
         test_de(code, &expected, &expected_json);
     }
 
@@ -670,7 +669,7 @@ mod test {
     fn test_vec() {
         let expected = vec![3, 2, 1];
         let expected_json = json!([3, 2, 1]);
-        let code = c_str!("[3, 2, 1]");
+        let code = c"[3, 2, 1]";
         test_de(code, &expected, &expected_json);
     }
 
@@ -678,7 +677,7 @@ mod test {
     fn test_vec_from_tuple() {
         let expected = vec![3, 2, 1];
         let expected_json = json!([3, 2, 1]);
-        let code = c_str!("(3, 2, 1)");
+        let code = c"(3, 2, 1)";
         test_de(code, &expected, &expected_json);
     }
 
@@ -686,7 +685,7 @@ mod test {
     fn test_hashmap() {
         let expected = hashmap! {"foo".to_string() => 4};
         let expected_json = json!({"foo": 4 });
-        let code = c_str!("{'foo': 4}");
+        let code = c"{'foo': 4}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -699,7 +698,7 @@ mod test {
 
         let expected = Foo::Variant;
         let expected_json = json!("Variant");
-        let code = c_str!("'Variant'");
+        let code = c"'Variant'";
         test_de(code, &expected, &expected_json);
     }
 
@@ -712,7 +711,7 @@ mod test {
 
         let expected = Foo::Tuple(12, "cat".to_string());
         let expected_json = json!({"Tuple": [12, "cat"]});
-        let code = c_str!("{'Tuple': [12, 'cat']}");
+        let code = c"{'Tuple': [12, 'cat']}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -725,7 +724,7 @@ mod test {
 
         let expected = Foo::NewType("cat".to_string());
         let expected_json = json!({"NewType": "cat" });
-        let code = c_str!("{'NewType': 'cat'}");
+        let code = c"{'NewType': 'cat'}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -741,7 +740,7 @@ mod test {
             bar: 25,
         };
         let expected_json = json!({"Struct": {"foo": "cat", "bar": 25 }});
-        let code = c_str!("{'Struct': {'foo': 'cat', 'bar': 25}}");
+        let code = c"{'Struct': {'foo': 'cat', 'bar': 25}}";
         test_de(code, &expected, &expected_json);
     }
     #[test]
@@ -754,7 +753,7 @@ mod test {
 
         let expected = Foo::Tuple(12.0, 'c');
         let expected_json = json!([12.0, 'c']);
-        let code = c_str!("[12.0, 'c']");
+        let code = c"[12.0, 'c']";
         test_de(code, &expected, &expected_json);
     }
 
@@ -768,7 +767,7 @@ mod test {
 
         let expected = Foo::NewType("cat".to_string());
         let expected_json = json!("cat");
-        let code = c_str!("'cat'");
+        let code = c"'cat'";
         test_de(code, &expected, &expected_json);
     }
 
@@ -785,7 +784,7 @@ mod test {
             bar: [2, 5, 3, 1],
         };
         let expected_json = json!({"foo": ["a", "b", "c"], "bar": [2, 5, 3, 1]});
-        let code = c_str!("{'foo': ['a', 'b', 'c'], 'bar': [2, 5, 3, 1]}");
+        let code = c"{'foo': ['a', 'b', 'c'], 'bar': [2, 5, 3, 1]}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -818,8 +817,7 @@ mod test {
         };
         let expected_json =
             json!({"name": "SomeFoo", "bar": { "value": 13, "variant": { "Tuple": [-1.5, 8]}}});
-        let code =
-            c_str!("{'name': 'SomeFoo', 'bar': {'value': 13, 'variant': {'Tuple': [-1.5, 8]}}}");
+        let code = c"{'name': 'SomeFoo', 'bar': {'value': 13, 'variant': {'Tuple': [-1.5, 8]}}}";
         test_de(code, &expected, &expected_json);
     }
 
@@ -868,7 +866,7 @@ mod test {
     fn test_char() {
         let expected = 'a';
         let expected_json = json!("a");
-        let code = c_str!("'a'");
+        let code = c"'a'";
         test_de(code, &expected, &expected_json);
     }
 
diff --git a/src/ser.rs b/src/ser.rs
index c8e6dd1..dc62154 100644
--- a/src/ser.rs
+++ b/src/ser.rs
@@ -622,7 +622,6 @@ impl<'py, P: PythonizeTypes> ser::SerializeStructVariant for PythonStructVariant
 mod test {
     use super::pythonize;
     use maplit::hashmap;
-    use pyo3::ffi::c_str;
     use pyo3::prelude::*;
     use pyo3::pybacked::PyBackedStr;
     use pyo3::types::{PyBytes, PyDict};
@@ -639,7 +638,7 @@ mod test {
             locals.set_item("obj", obj)?;
 
             py.run(
-                c_str!("import json; result = json.dumps(obj, separators=(',', ':'))"),
+                c"import json; result = json.dumps(obj, separators=(',', ':'))",
                 None,
                 Some(&locals),
             )?;
diff --git a/tests/test_with_serde_path_to_err.rs b/tests/test_with_serde_path_to_err.rs
index 82fd8bb..504dae9 100644
--- a/tests/test_with_serde_path_to_err.rs
+++ b/tests/test_with_serde_path_to_err.rs
@@ -102,7 +102,7 @@ fn test_de_invalid() {
         assert_eq!(err.path().to_string(), "root_map.nested_1.nested_key");
         assert_eq!(
             err.to_string(),
-            "root_map.nested_1.nested_key: unexpected type: 'int' object cannot be cast as 'str'"
+            "root_map.nested_1.nested_key: unexpected type: 'int' object is not an instance of 'str'"
         );
     })
 }