diff --git a/oximeter/db/src/lib.rs b/oximeter/db/src/lib.rs
index d57fcdc525..4fa241af74 100644
--- a/oximeter/db/src/lib.rs
+++ b/oximeter/db/src/lib.rs
@@ -328,17 +328,20 @@ pub struct TimeseriesPageSelector {
 pub(crate) type TimeseriesKey = u64;
 
 pub(crate) fn timeseries_key(sample: &Sample) -> TimeseriesKey {
-    timeseries_key_for(sample.target_fields(), sample.metric_fields())
+    timeseries_key_for(
+        sample.sorted_target_fields(),
+        sample.sorted_metric_fields(),
+    )
 }
 
-pub(crate) fn timeseries_key_for<'a>(
-    target_fields: impl Iterator<Item = &'a Field>,
-    metric_fields: impl Iterator<Item = &'a Field>,
+fn timeseries_key_for<'a>(
+    target_fields: &BTreeMap<String, Field>,
+    metric_fields: &BTreeMap<String, Field>,
 ) -> TimeseriesKey {
     use highway::HighwayHasher;
     use std::hash::{Hash, Hasher};
     let mut hasher = HighwayHasher::default();
-    for field in target_fields.chain(metric_fields) {
+    for field in target_fields.values().chain(metric_fields.values()) {
         bcs::to_bytes(&field)
             .expect("Failed to serialized field to bytes")
             .hash(&mut hasher);
@@ -460,10 +463,12 @@ mod tests {
 
         let mut output = vec![];
         for (name, value) in values {
-            let key = timeseries_key_for(
-                [&Field { name: name.to_string(), value }].into_iter(),
-                [].into_iter(),
-            );
+            let target_fields = BTreeMap::from([(
+                "field".to_string(),
+                Field { name: name.to_string(), value },
+            )]);
+            let metric_fields = BTreeMap::new();
+            let key = timeseries_key_for(&target_fields, &metric_fields);
             output.push(format!("{name} -> {key}"));
         }
 
diff --git a/oximeter/oximeter/src/types.rs b/oximeter/oximeter/src/types.rs
index 1c8af6f83e..d3f1b9e746 100644
--- a/oximeter/oximeter/src/types.rs
+++ b/oximeter/oximeter/src/types.rs
@@ -769,6 +769,11 @@ impl Sample {
         self.target.fields.values()
     }
 
+    /// Return the sorted fields of this sample's target.
+    pub fn sorted_target_fields(&self) -> &BTreeMap<String, Field> {
+        &self.target.fields
+    }
+
     /// Return the name of this sample's metric.
     pub fn metric_name(&self) -> &str {
         &self.metric.name
@@ -779,6 +784,11 @@ impl Sample {
         self.metric.fields.values()
     }
 
+    /// Return the sorted fields of this sample's metric
+    pub fn sorted_metric_fields(&self) -> &BTreeMap<String, Field> {
+        &self.metric.fields
+    }
+
     // Check validity of field names for the target and metric. Currently this
     // just verifies there are no duplicate names between them.
     fn verify_field_names(