diff --git a/ingester/src/dml_sink/mock_sink.rs b/ingester/src/dml_sink/mock_sink.rs
index 5f8c5ca0a0..f489e1f702 100644
--- a/ingester/src/dml_sink/mock_sink.rs
+++ b/ingester/src/dml_sink/mock_sink.rs
@@ -4,13 +4,13 @@ use async_trait::async_trait;
 use dml::DmlOperation;
 use parking_lot::Mutex;
 
-use super::DmlSink;
+use super::{DmlError, DmlSink};
 use crate::data::DmlApplyAction;
 
 #[derive(Debug, Default)]
 struct MockDmlSinkState {
     calls: Vec<DmlOperation>,
-    ret: VecDeque<Result<DmlApplyAction, crate::data::Error>>,
+    ret: VecDeque<Result<DmlApplyAction, DmlError>>,
 }
 
 #[derive(Debug, Default)]
@@ -19,9 +19,9 @@ pub struct MockDmlSink {
 }
 
 impl MockDmlSink {
-    pub fn with_apply_return(
+    pub(crate) fn with_apply_return(
         self,
-        ret: impl Into<VecDeque<Result<DmlApplyAction, crate::data::Error>>>,
+        ret: impl Into<VecDeque<Result<DmlApplyAction, DmlError>>>,
     ) -> Self {
         self.state.lock().ret = ret.into();
         self
@@ -34,7 +34,8 @@ impl MockDmlSink {
 
 #[async_trait]
 impl DmlSink for MockDmlSink {
-    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, crate::data::Error> {
+    type Error = DmlError;
+    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, DmlError> {
         let mut state = self.state.lock();
         state.calls.push(op);
         state.ret.pop_front().expect("no mock sink value to return")
diff --git a/ingester/src/dml_sink/trait.rs b/ingester/src/dml_sink/trait.rs
index 1202271c8a..964c494b8a 100644
--- a/ingester/src/dml_sink/trait.rs
+++ b/ingester/src/dml_sink/trait.rs
@@ -1,17 +1,27 @@
-use std::{fmt::Debug, ops::Deref, sync::Arc};
+use std::{error::Error, fmt::Debug, ops::Deref, sync::Arc};
 
 use async_trait::async_trait;
 use dml::DmlOperation;
+use thiserror::Error;
 
 use crate::data::DmlApplyAction;
 
+#[derive(Debug, Error)]
+pub(crate) enum DmlError {
+    /// An error applying a [`DmlOperation`].
+    #[error(transparent)]
+    Data(#[from] crate::data::Error),
+}
+
 /// A [`DmlSink`] handles [`DmlOperation`] instances read from a shard.
 #[async_trait]
 pub(crate) trait DmlSink: Debug + Send + Sync {
+    type Error: Error + Into<DmlError> + Send;
+
     /// Apply `op` read from a shard, returning `Ok(DmlApplyAction::Applied(bool))`, the bool indicating if the
     /// ingest should be paused. Returns `Ok(DmlApplyAction::Skipped)` if the operation has been
     /// applied previously and was skipped.
-    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, crate::data::Error>;
+    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, Self::Error>;
 }
 
 #[async_trait]
@@ -19,7 +29,8 @@ impl<T> DmlSink for Arc<T>
 where
     T: DmlSink,
 {
-    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, crate::data::Error> {
+    type Error = T::Error;
+    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, Self::Error> {
         self.deref().apply(op).await
     }
 }
diff --git a/ingester/src/server/grpc/rpc_write.rs b/ingester/src/server/grpc/rpc_write.rs
index 26956d6464..18a8566af1 100644
--- a/ingester/src/server/grpc/rpc_write.rs
+++ b/ingester/src/server/grpc/rpc_write.rs
@@ -9,7 +9,10 @@ use observability_deps::tracing::*;
 use thiserror::Error;
 use tonic::{Request, Response};
 
-use crate::{data::DmlApplyAction, dml_sink::DmlSink};
+use crate::{
+    data::DmlApplyAction,
+    dml_sink::{DmlError, DmlSink},
+};
 
 // A list of error states when handling an RPC write request.
 //
@@ -29,7 +32,7 @@ enum RpcError {
     Decode(mutable_batch_pb::decode::Error),
 
     #[error(transparent)]
-    Apply(crate::data::Error),
+    Apply(DmlError),
 }
 
 impl From<RpcError> for tonic::Status {
@@ -40,8 +43,10 @@ impl From<RpcError> for tonic::Status {
             RpcError::Decode(_) | RpcError::NoPayload | RpcError::NoTables => {
                 Self::invalid_argument(e.to_string())
             }
-            RpcError::Apply(Error::BufferWrite { source }) => map_write_error(source),
-            RpcError::Apply(Error::ShardNotFound { .. }) => {
+            RpcError::Apply(DmlError::Data(Error::BufferWrite { source })) => {
+                map_write_error(source)
+            }
+            RpcError::Apply(DmlError::Data(Error::ShardNotFound { .. })) => {
                 // This is not a reachable error state in the gRPC write model,
                 // and is enumerated here purely because of error conflation
                 // (one big error type instead of small, composable errors).
@@ -159,7 +164,7 @@ where
             }
             Err(e) => {
                 error!(error=%e, "failed to apply DML op");
-                return Err(RpcError::Apply(e))?;
+                return Err(RpcError::Apply(e.into()))?;
             }
         }
 
diff --git a/ingester/src/stream_handler/handler.rs b/ingester/src/stream_handler/handler.rs
index ed46e42a78..58d3bdfc89 100644
--- a/ingester/src/stream_handler/handler.rs
+++ b/ingester/src/stream_handler/handler.rs
@@ -510,7 +510,7 @@ fn metric_attrs(
 mod tests {
     use super::*;
     use crate::{
-        dml_sink::mock_sink::MockDmlSink,
+        dml_sink::{mock_sink::MockDmlSink, DmlError},
         lifecycle::{LifecycleConfig, LifecycleManager},
     };
     use assert_matches::assert_matches;
@@ -996,7 +996,7 @@ mod tests {
             Ok(DmlOperation::Write(make_write(2222, 2)))
         ]],
         sink_rets = [
-            Err(crate::data::Error::ShardNotFound{shard_id: ShardId::new(42)}),
+            Err(DmlError::Data(crate::data::Error::ShardNotFound{shard_id: ShardId::new(42)})),
             Ok(DmlApplyAction::Applied(true)),
         ],
         want_ttbr = 2,
diff --git a/ingester/src/stream_handler/sink_adaptor.rs b/ingester/src/stream_handler/sink_adaptor.rs
index 30490ccf75..99c6b3bd26 100644
--- a/ingester/src/stream_handler/sink_adaptor.rs
+++ b/ingester/src/stream_handler/sink_adaptor.rs
@@ -38,7 +38,9 @@ impl IngestSinkAdaptor {
 
 #[async_trait]
 impl DmlSink for IngestSinkAdaptor {
-    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, crate::data::Error> {
+    type Error = crate::data::Error;
+
+    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, Self::Error> {
         self.ingest_data
             .buffer_operation(self.shard_id, op, &self.lifecycle_handle)
             .await
diff --git a/ingester/src/stream_handler/sink_instrumentation.rs b/ingester/src/stream_handler/sink_instrumentation.rs
index b7548bf583..8405d8a9a2 100644
--- a/ingester/src/stream_handler/sink_instrumentation.rs
+++ b/ingester/src/stream_handler/sink_instrumentation.rs
@@ -155,7 +155,9 @@ where
     T: DmlSink,
     P: TimeProvider,
 {
-    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, crate::data::Error> {
+    type Error = T::Error;
+
+    async fn apply(&self, op: DmlOperation) -> Result<DmlApplyAction, Self::Error> {
         let meta = op.meta();
 
         // Immediately increment the "bytes read" metric as it records the
@@ -236,7 +238,7 @@ where
 mod tests {
     use super::*;
     use crate::{
-        dml_sink::mock_sink::MockDmlSink,
+        dml_sink::{mock_sink::MockDmlSink, DmlError},
         stream_handler::mock_watermark_fetcher::MockWatermarkFetcher,
     };
     use assert_matches::assert_matches;
@@ -302,9 +304,9 @@ mod tests {
     async fn test(
         op: impl Into<DmlOperation> + Send,
         metrics: &metric::Registry,
-        with_sink_return: Result<DmlApplyAction, crate::data::Error>,
+        with_sink_return: Result<DmlApplyAction, DmlError>,
         with_fetcher_return: Option<i64>,
-    ) -> Result<DmlApplyAction, crate::data::Error> {
+    ) -> Result<DmlApplyAction, DmlError> {
         let op = op.into();
         let inner = MockDmlSink::default().with_apply_return([with_sink_return]);
         let instrumentation = SinkInstrumentation::new(
@@ -420,13 +422,16 @@ mod tests {
         let got = test(
             op,
             &metrics,
-            Err(crate::data::Error::ShardNotFound {
+            Err(DmlError::Data(crate::data::Error::ShardNotFound {
                 shard_id: ShardId::new(42),
-            }),
+            })),
             Some(12345),
         )
         .await;
-        assert_matches!(got, Err(crate::data::Error::ShardNotFound { .. }));
+        assert_matches!(
+            got,
+            Err(DmlError::Data(crate::data::Error::ShardNotFound { .. }))
+        );
 
         // Validate the various write buffer metrics
         assert_matches!(