diff --git a/promql/engine.go b/promql/engine.go
index 6ba6008b19..07fb03d66c 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -1175,7 +1175,7 @@ func (ev *evaluator) Eval(ctx context.Context, expr parser.Expr) (v parser.Value
 
 	v, ws = ev.eval(ctx, expr)
 	if ev.enableDelayedNameRemoval {
-		ev.cleanupMetricLabels(v)
+		v = ev.cleanupMetricLabels(v)
 	}
 	return v, ws, nil
 }
@@ -3832,7 +3832,7 @@ func (*evaluator) aggregationCountValues(e *parser.AggregateExpr, grouping []str
 	return enh.Out, nil
 }
 
-func (ev *evaluator) cleanupMetricLabels(v parser.Value) {
+func (ev *evaluator) cleanupMetricLabels(v parser.Value) parser.Value {
 	if v.Type() == parser.ValueTypeMatrix {
 		mat := v.(Matrix)
 		for i := range mat {
@@ -3840,9 +3840,7 @@ func (ev *evaluator) cleanupMetricLabels(v parser.Value) {
 				mat[i].Metric = mat[i].Metric.DropReserved(schema.IsMetadataLabel)
 			}
 		}
-		if mat.ContainsSameLabelset() {
-			ev.errorf("vector cannot contain metrics with the same labelset")
-		}
+		return ev.mergeSeriesWithSameLabelset(mat)
 	} else if v.Type() == parser.ValueTypeVector {
 		vec := v.(Vector)
 		for i := range vec {
@@ -3853,7 +3851,75 @@ func (ev *evaluator) cleanupMetricLabels(v parser.Value) {
 		if vec.ContainsSameLabelset() {
 			ev.errorf("vector cannot contain metrics with the same labelset")
 		}
+		return vec
+	}
+	return v
+}
+
+// mergeSeriesWithSameLabelset merges series in a matrix that have the same labelset
+// after __name__ label removal. This happens when delayed name removal is enabled and
+// operations like OR combine series that originally had different names but end up
+// with the same labelset after dropping the name. If series with the same labelset
+// have overlapping timestamps, an error is returned.
+func (ev *evaluator) mergeSeriesWithSameLabelset(mat Matrix) Matrix {
+	if len(mat) <= 1 {
+		return mat
+	}
+
+	// Fast path: check if there are any duplicate labelsets without allocating.
+	// This is the common case and we want to avoid allocations.
+	if !mat.ContainsSameLabelset() {
+		return mat
 	}
+
+	// Slow path: there are duplicates, so we need to merge series with non-overlapping timestamps.
+	// Group series by their labelset hash.
+	seriesByHash := make(map[uint64][]int)
+	for i := range mat {
+		hash := mat[i].Metric.Hash()
+		seriesByHash[hash] = append(seriesByHash[hash], i)
+	}
+
+	// Merge series with the same labelset.
+	merged := make(Matrix, 0, len(seriesByHash))
+	for _, indices := range seriesByHash {
+		if len(indices) == 1 {
+			// No collision, add as-is.
+			merged = append(merged, mat[indices[0]])
+			continue
+		}
+
+		// Multiple series with the same labelset - merge all samples.
+		base := mat[indices[0]]
+		for _, idx := range indices[1:] {
+			base.Floats = append(base.Floats, mat[idx].Floats...)
+			base.Histograms = append(base.Histograms, mat[idx].Histograms...)
+		}
+
+		// Sort merged samples by timestamp.
+		sort.Slice(base.Floats, func(i, j int) bool {
+			return base.Floats[i].T < base.Floats[j].T
+		})
+		sort.Slice(base.Histograms, func(i, j int) bool {
+			return base.Histograms[i].T < base.Histograms[j].T
+		})
+
+		// Check for duplicate timestamps in sorted samples.
+		for i := 1; i < len(base.Floats); i++ {
+			if base.Floats[i].T == base.Floats[i-1].T {
+				ev.errorf("vector cannot contain metrics with the same labelset")
+			}
+		}
+		for i := 1; i < len(base.Histograms); i++ {
+			if base.Histograms[i].T == base.Histograms[i-1].T {
+				ev.errorf("vector cannot contain metrics with the same labelset")
+			}
+		}
+
+		merged = append(merged, base)
+	}
+
+	return merged
 }
 
 func addToSeries(ss *Series, ts int64, f float64, h *histogram.FloatHistogram, numSteps int) {
diff --git a/promql/promqltest/testdata/name_label_dropping.test b/promql/promqltest/testdata/name_label_dropping.test
index 3a6f4098df..e0180c7ffe 100644
--- a/promql/promqltest/testdata/name_label_dropping.test
+++ b/promql/promqltest/testdata/name_label_dropping.test
@@ -126,3 +126,13 @@ eval instant at 10m sum by (__name__) (metric_total{env="3"} or rate(metric_tota
 # Same as above, but with reversed order.
 eval instant at 10m sum by (__name__) (rate(metric_total{env="3"}[5m]) or metric_total{env="1"})
   metric_total 10
+
+clear
+
+# Test delayed name removal with range queries and OR operator.
+load 10m
+  metric_a 1 _
+  metric_b 3 4
+
+eval range from 0 to 20m step 10m -metric_a or -metric_b
+  {} -1 -4 _