diff --git a/crates/twirp/src/error.rs b/crates/twirp/src/error.rs
index 3b22602..7c8ecc1 100644
--- a/crates/twirp/src/error.rs
+++ b/crates/twirp/src/error.rs
@@ -199,7 +199,7 @@ impl TwirpErrorResponse {
         &mut self.meta
     }
 
-    pub fn with_meta<S: ToString>(mut self, key: S, value: S) -> Self {
+    pub fn with_meta<S1: ToString, S2: ToString>(mut self, key: S1, value: S2) -> Self {
         self.meta.insert(key.to_string(), value.to_string());
         self
     }
diff --git a/crates/twirp/src/server.rs b/crates/twirp/src/server.rs
index eb140b2..ea9ba73 100644
--- a/crates/twirp/src/server.rs
+++ b/crates/twirp/src/server.rs
@@ -63,7 +63,7 @@ where
         Ok(tuple) => tuple,
         Err(err) => {
             return error::malformed("bad request")
-                .with_meta("error", &err.to_string())
+                .with_meta("error", &err)
                 .with_generic_error(err)
                 .into_response();
         }
@@ -77,7 +77,7 @@ where
         Ok(resp) => resp,
         Err(err) => {
             return error::internal("error serializing response")
-                .with_meta("error", &err.to_string())
+                .with_meta("error", &err)
                 .with_generic_error(err)
                 .into_response();
         }