diff --git a/src/promql/src/histogram_eval/aggregate.rs b/src/promql/src/histogram_eval/aggregate.rs
index 5640ea30066..6653c5a40b6 100644
--- a/src/promql/src/histogram_eval/aggregate.rs
+++ b/src/promql/src/histogram_eval/aggregate.rs
@@ -128,33 +128,31 @@ fn aggregate_point<'a>(
         if incompatible {
             continue;
         }
+        // The only addition error Go's `handleAggregationError` absorbs; others propagate.
+        if current.uses_custom_buckets() != h.uses_custom_buckets() {
+            incompatible = true;
+            continue;
+        }
         match op {
-            HistogramAggregate::Sum => match current.kahan_add(&h, compensation.take()) {
-                Ok((c, _)) => compensation = Some(c),
-                Err(_) => incompatible = true,
-            },
+            HistogramAggregate::Sum => {
+                let (c, _) = current.kahan_add(&h, compensation.take())?;
+                compensation = Some(c);
+            }
             HistogramAggregate::Avg => {
                 if mean.is_none() {
                     let mut sum = current.clone();
-                    match sum.kahan_add(&h, compensation.clone()) {
-                        Ok((c, _)) if !sum.has_overflow() => {
-                            *current = sum;
-                            compensation = Some(c);
-                            continue;
-                        }
-                        Ok(_) => {
-                            let mut started = current.clone();
-                            started.div(count - 1.0);
-                            if let Some(c) = compensation.as_mut() {
-                                c.div(count - 1.0);
-                            }
-                            mean = Some(started);
-                        }
-                        Err(_) => {
-                            incompatible = true;
-                            continue;
-                        }
+                    let (c, _) = sum.kahan_add(&h, compensation.clone())?;
+                    if !sum.has_overflow() {
+                        *current = sum;
+                        compensation = Some(c);
+                        continue;
                     }
+                    let mut started = current.clone();
+                    started.div(count - 1.0);
+                    if let Some(c) = compensation.as_mut() {
+                        c.div(count - 1.0);
+                    }
+                    mean = Some(started);
                 }
                 // Go switches to an incremental mean once the plain sum overflows.
                 let q = (count - 1.0) / count;
@@ -165,10 +163,8 @@ fn aggregate_point<'a>(
                 to_add.div(count);
                 let mean = mean.as_mut().expect("set above");
                 mean.mul(q);
-                match mean.kahan_add(&to_add, compensation.take()) {
-                    Ok((c, _)) => compensation = Some(c),
-                    Err(_) => incompatible = true,
-                }
+                let (c, _) = mean.kahan_add(&to_add, compensation.take())?;
+                compensation = Some(c);
             }
         }
     }
diff --git a/src/promql/src/histogram_eval/float_histogram.rs b/src/promql/src/histogram_eval/float_histogram.rs
index 1f984c4635a..ce10ae67ff8 100644
--- a/src/promql/src/histogram_eval/float_histogram.rs
+++ b/src/promql/src/histogram_eval/float_histogram.rs
@@ -679,8 +679,6 @@ fn iterate(side: &Buckets, schema: i32, target: i32, threshold: f64) -> Result<B
         let target_idx = target_index(idx, schema, target);
         match out.last_mut() {
             Some(last) if schema != target && last.0 == target_idx => last.1 += count,
-            // A merged bucket starts its sum from zero.
-            _ if schema != target => out.push((target_idx, 0.0 + count)),
             _ => out.push((target_idx, count)),
         }
     }
diff --git a/src/promql/src/histogram_eval/tests.rs b/src/promql/src/histogram_eval/tests.rs
index 4d2c47c22ff..42640548919 100644
--- a/src/promql/src/histogram_eval/tests.rs
+++ b/src/promql/src/histogram_eval/tests.rs
@@ -691,3 +691,54 @@ fn widened_zero_threshold_uses_go_bounds() {
     ));
     assert!(!current.detect_reset(&previous).unwrap());
 }
+
+/// Only mixing exponential and custom buckets ends a group without a result; any other
+/// addition error, such as an invalid layout, fails the aggregation.
+#[test]
+fn aggregation_propagates_errors_other_than_mixed_schemas() {
+    let grid = Arc::new(
+        datatypes::series::time::EvalGrid::try_new(
+            datatypes::series::time::GridSpec::try_new(0, 1_000, 1).unwrap(),
+        )
+        .unwrap(),
+    );
+    let schema = Arc::new(SeriesSchema {
+        fields: vec![FieldSpec {
+            name: Arc::from("value"),
+        }]
+        .into(),
+        eval_grid: Some(grid),
+    });
+    let group = |texts: [&str; 2]| -> Vec<Series> {
+        texts
+            .iter()
+            .enumerate()
+            .map(|(host, text)| {
+                let labels = Labels::from([("host".to_string(), host.to_string())]);
+                let histograms = BTreeMap::from([(0, text.to_string())]);
+                mixed_series(&schema, &labels, &BTreeMap::new(), &histograms).unwrap()
+            })
+            .collect()
+    };
+    let exponential = "0/0/0/3ff0000000000000/3ff0000000000000/0/1_1/3ff0000000000000///";
+    let custom =
+        "-53/0/0/3ff0000000000000/3ff0000000000000/0/0_1/3ff0000000000000///3ff0000000000000";
+    let invalid =
+        "9/3ff0000000000000/0/3ff0000000000000/3ff0000000000000/0/1_1/3ff0000000000000///";
+    for op in [HistogramAggregate::Sum, HistogramAggregate::Avg] {
+        let mixed = aggregate_histograms(
+            op,
+            &schema,
+            &group([exponential, custom]),
+            metric_of(&Labels::new()),
+        );
+        assert!(mixed.unwrap().is_none());
+        let invalid = aggregate_histograms(
+            op,
+            &schema,
+            &group([invalid, invalid]),
+            metric_of(&Labels::new()),
+        );
+        assert!(invalid.is_err());
+    }
+}