diff --git a/python/msgspec_toon/__init__.py b/python/msgspec_toon/__init__.py
index c1e732c..0c2d0cb 100644
--- a/python/msgspec_toon/__init__.py
+++ b/python/msgspec_toon/__init__.py
@@ -37,6 +37,18 @@
 
 EncodeError: Final = msgspec.EncodeError
 
+_NON_STRING_KEY_ERROR: Final = (
+    "object keys must be strings; convert with msgspec.to_builtins(..., str_keys=True)"
+)
+
+
+def _new_encode_error(message: str) -> msgspec.EncodeError:
+    """Translate stable native error codes without changing native hot-path layout."""
+    if message == "object keys must be strings":
+        message = _NON_STRING_KEY_ERROR
+    return msgspec.EncodeError(message)
+
+
 # Stable type identities and the exact-pinned msgspec datetime normalizer.
 _NATIVE_SCALAR_TYPES: Final = (
     datetime.datetime,
@@ -271,7 +283,7 @@ def __init__(
             enc_hook=native_hook,
             plan_source=encode_plan_for,
             struct_base=msgspec.Struct,
-            encode_error=msgspec.EncodeError,
+            encode_error=_new_encode_error,
             delimiter=delimiter,
             indent=indent,
         )
diff --git a/src/encode.rs b/src/encode.rs
index 3cfc3f7..9f3f2d6 100644
--- a/src/encode.rs
+++ b/src/encode.rs
@@ -26,8 +26,6 @@ use crate::writer::Writer;
 const CELL_WIDTH_ESTIMATE: usize = 10;
 
 const MAX_HOOK_DEPTH: usize = 8;
-const NON_STRING_KEY_ERROR: &str =
-    "object keys must be strings; convert with msgspec.to_builtins(..., str_keys=True)";
 
 pub struct EncodeContext {
     pub enc_hook: Option<Py<PyAny>>,
@@ -406,7 +404,7 @@ fn object_pairs<'value, 'py>(
             let mut pairs = Vec::with_capacity(map.len());
             for (key, item) in map.iter() {
                 let Ok(key_text) = key.cast_into::<PyString>() else {
-                    return Err(encode_err(ctx, py, NON_STRING_KEY_ERROR));
+                    return Err(encode_err(ctx, py, "object keys must be strings"));
                 };
                 pairs.push((EntryText::Object(key_text), item));
             }
@@ -781,7 +779,7 @@ fn root_object_decision<'value, 'py>(
     let mut rows = (map.len() >= 2).then(|| Vec::with_capacity(map.len()));
     for (key, item) in map.iter() {
         let Ok(key_text) = key.cast_into::<PyString>() else {
-            return Err(encode_err(ctx, py, NON_STRING_KEY_ERROR));
+            return Err(encode_err(ctx, py, "object keys must be strings"));
         };
         if let Some(candidate_rows) = rows.as_mut() {
             if item.is_instance_of::<PyDict>() || item.is_instance(ctx.struct_base.bind(py))? {