diff --git a/Cargo.lock b/Cargo.lock
index 071e7d4f7..73787d2af 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1877,7 +1877,7 @@ dependencies = [
  "serde_json",
  "sha2 0.10.9",
  "tempfile",
- "thiserror 1.0.69",
+ "thiserror 2.0.18",
  "tiktoken-rs",
  "tokenizers",
  "toml",
@@ -1894,7 +1894,7 @@ dependencies = [
  "headroom-core",
  "serde",
  "serde_json",
- "thiserror 1.0.69",
+ "thiserror 2.0.18",
 ]
 
 [[package]]
@@ -1929,7 +1929,7 @@ dependencies = [
  "serde",
  "serde_json",
  "sha2 0.10.9",
- "thiserror 1.0.69",
+ "thiserror 2.0.18",
  "tokio",
  "tokio-stream",
  "tokio-tungstenite",
diff --git a/Cargo.toml b/Cargo.toml
index 8e19ed7c2..7896c1589 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -47,7 +47,7 @@ serde = { version = "1", features = ["derive"] }
 # Enabled here in Phase A so PR-B2 can land as a pure consumer change.
 serde_json = { version = "1", features = ["preserve_order", "arbitrary_precision", "raw_value"] }
 bytes = "1"
-thiserror = "1"
+thiserror = "2"
 # `log` compat: when no tracing subscriber is active (the case inside the
 # headroom-py cdylib), events are re-emitted as `log` records so pyo3-log
 # can forward them to Python's logging. No effect on binaries that install