diff --git a/Cargo.lock b/Cargo.lock
index 92169d96..1a6be9b8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -618,26 +618,6 @@ dependencies = [
  "unicode-ident",
 ]
 
-[[package]]
-name = "thiserror"
-version = "1.0.61"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c546c80d6be4bc6a00c0f01730c08df82eaa7a7a61f11d656526506112cc1709"
-dependencies = [
- "thiserror-impl",
-]
-
-[[package]]
-name = "thiserror-impl"
-version = "1.0.61"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46c3384250002a6d5af4d114f2845d37b57521033f30d5c3f46c4d70e1197533"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn",
-]
-
 [[package]]
 name = "tskit"
 version = "0.15.0-alpha.3"
@@ -656,7 +636,6 @@ dependencies = [
  "serde-pickle",
  "serde_json",
  "streaming-iterator",
- "thiserror",
  "tskit-derive",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index a43a771d..14ed5dd5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,6 @@ lto = "fat"
 codegen-units=1
 
 [dependencies]
-thiserror = "1.0"
 libc = "0.2.155"
 streaming-iterator = "0.1.5"
 serde = {version = "1.0.203", features = ["derive"], optional = true}
diff --git a/src/sys/mod.rs b/src/sys/mod.rs
index f508f090..89ef5fb6 100644
--- a/src/sys/mod.rs
+++ b/src/sys/mod.rs
@@ -1,5 +1,3 @@
-use thiserror::Error;
-
 mod macros;
 
 #[allow(dead_code)]
@@ -47,52 +45,76 @@ pub use treeseq::TreeSequence;
 
 use traits::TskTeardown;
 
-#[derive(Error, Debug)]
 #[non_exhaustive]
+#[derive(Debug)]
 pub enum TskitError {
     /// Returned when conversion attempts fail
-    #[error("range error: {}", *.0)]
     RangeError(String),
     /// Used when bad input is encountered.
-    #[error("we received {} but expected {}",*got, *expected)]
     ValueError { got: String, expected: String },
     /// Used when array access is out of range.
     /// Typically, this is used when accessing
     /// arrays allocated on the C side.
-    #[error("Invalid index")]
     IndexError,
     /// Raised when samples are requested from
     /// [`crate::Tree`] objects, but sample lists are
     /// not being updated.
-    #[error("Not tracking samples in Trees")]
     NotTrackingSamples,
     /// Wrapper around tskit C API error codes.
-    #[error("{}", get_tskit_error_message(*code))]
     ErrorCode { code: i32 },
     /// A redirection of [``crate::metadata::MetadataError``]
-    #[error("{value:?}")]
     MetadataError {
         /// The redirected error
-        #[from]
         value: MetadataError,
     },
     /// General error variant
-    #[error("{}", *.0)]
     LibraryError(String),
 }
 
-#[derive(Error, Debug)]
+impl std::fmt::Display for TskitError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::RangeError(msg) => write!(f, "range error: {}", msg),
+            Self::ValueError { got, expected } => {
+                write!(f, "we received {} but expected {}", got, expected)
+            }
+            Self::IndexError => write!(f, "Invalid index"),
+            Self::NotTrackingSamples => write!(f, "Not tracking samples in Trees"),
+            Self::ErrorCode { code } => write!(f, "{}", get_tskit_error_message(*code)),
+            Self::MetadataError { value } => write!(f, "meta data error: {}", value),
+            Self::LibraryError(msg) => write!(f, "library error: {msg}"),
+        }
+    }
+}
+
+impl From<MetadataError> for TskitError {
+    fn from(value: MetadataError) -> Self {
+        Self::MetadataError { value }
+    }
+}
+
+impl std::error::Error for TskitError {}
+
+#[derive(Debug)]
 #[non_exhaustive]
 pub enum MetadataError {
     /// Error related to types implementing
     /// metadata serialization.
-    #[error("{}", *value)]
     RoundtripError {
-        #[from]
         value: Box<dyn std::error::Error + Send + Sync>,
     },
 }
 
+impl std::fmt::Display for MetadataError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::RoundtripError { value } => write!(f, "metadata round trip error: {value:?}"),
+        }
+    }
+}
+
+impl std::error::Error for MetadataError {}
+
 //#[non_exhaustive]
 //#[derive(Error, Debug)]
 //pub enum Error {