diff --git a/promql/engine.go b/promql/engine.go
index c762c1b6a5..bb1536829e 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -3444,21 +3444,24 @@ func trimHistogram(trimmedHist *histogram.FloatHistogram, rhs float64, isUpperTr
 	}
 }
 
-func computeMidpoint(survivingIntervalBoundA, survivingIntervalBoundB float64, isPositive, isLinear bool) float64 {
-	if math.IsInf(survivingIntervalBoundA, 0) {
-		if math.IsInf(survivingIntervalBoundB, 0) {
+func computeMidpoint(survivingIntervalLowerBound, survivingIntervalUpperBound float64, isPositive, isLinear bool) float64 {
+	if math.IsInf(survivingIntervalLowerBound, 0) {
+		if math.IsInf(survivingIntervalUpperBound, 0) {
 			return 0
 		}
-		return survivingIntervalBoundB
-	} else if math.IsInf(survivingIntervalBoundB, 0) {
-		return survivingIntervalBoundA
+		if survivingIntervalUpperBound > 0 {
+			return survivingIntervalUpperBound / 2
+		}
+		return survivingIntervalUpperBound
+	} else if math.IsInf(survivingIntervalUpperBound, 0) {
+		return survivingIntervalLowerBound
 	}
 
 	if isLinear {
-		return (survivingIntervalBoundA + survivingIntervalBoundB) / 2
+		return (survivingIntervalLowerBound + survivingIntervalUpperBound) / 2
 	}
 
-	geoMean := math.Sqrt(math.Abs(survivingIntervalBoundA * survivingIntervalBoundB))
+	geoMean := math.Sqrt(math.Abs(survivingIntervalLowerBound * survivingIntervalUpperBound))
 
 	if isPositive {
 		return geoMean
diff --git a/promql/promqltest/testdata/native_histograms.test b/promql/promqltest/testdata/native_histograms.test
index d9eaf4e23f..614521b3af 100644
--- a/promql/promqltest/testdata/native_histograms.test
+++ b/promql/promqltest/testdata/native_histograms.test
@@ -2020,24 +2020,24 @@ load 1m
 
 # Custom buckets: trim on bucket boundary without interpolation
 eval instant at 1m cbh </ 15
-  cbh{} {{schema:-53 count:11 sum:100 custom_values:[5 10 15 20] buckets:[1 6 4]}}
+  cbh{} {{schema:-53 count:11 sum:97.5 custom_values:[5 10 15 20] buckets:[1 6 4]}}
 
 eval instant at 1m cbh >/ 15
   cbh{} {{schema:-53 count:4 sum:72.5 custom_values:[5 10 15 20] offset:3 buckets:[3 1]}}
 
 # Custom buckets: trim uses linear interpolation if cutoff is inside a bucket
 eval instant at 1m cbh </ 13
-  cbh{} {{schema:-53 count:9.4 sum:77.6 custom_values:[5 10 15 20] buckets:[1 6 2.4]}}
+  cbh{} {{schema:-53 count:9.4 sum:75.1 custom_values:[5 10 15 20] buckets:[1 6 2.4]}}
 
 eval instant at 1m cbh >/ 13
   cbh{} {{schema:-53 count:5.6 sum:94.9 custom_values:[5 10 15 20] offset:2 buckets:[1.6 3 1]}}
 
 eval instant at 1m cbh </ 7.5
-  cbh{} {{schema:-53 count:4 sum:23.75 custom_values:[5 10 15 20] buckets:[1 3]}}
+  cbh{} {{schema:-53 count:4 sum:21.25 custom_values:[5 10 15 20] buckets:[1 3]}}
 
 # Custom buckets: trim drops +Inf bucket entirely even if cutoff is above its lower bound
 eval instant at 1m cbh </ 50
-  cbh{} {{schema:-53 count:14 sum:152.5 custom_values:[5 10 15 20] buckets:[1 6 4 3]}}
+  cbh{} {{schema:-53 count:14 sum:150.0 custom_values:[5 10 15 20] buckets:[1 6 4 3]}}
 
 eval instant at 1m cbh </ -Inf
   cbh{} {{schema:-53 custom_values:[5 10 15 20]}}
@@ -2145,7 +2145,7 @@ load 1m
 
 # Skip (5; +Inf] bucket (100).
 eval instant at 1m cbh_two_buckets_split_at_positive </ 10.0
-  cbh_two_buckets_split_at_positive {{schema:-53 sum:5.0 count:1 custom_values:[5] buckets:[1 0]}}
+  cbh_two_buckets_split_at_positive {{schema:-53 sum:2.5 count:1 custom_values:[5] buckets:[1 0]}}
 
 # Skip (5; +Inf] bucket (100) and 3/5 of [-Inf, 5] bucket (0.6 * 3.5).
 eval instant at 1m cbh_two_buckets_split_at_positive </ 2.0