diff --git a/promql/engine.go b/promql/engine.go
index 07fb03d66c..5a08da121c 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -2191,8 +2191,8 @@ func (ev *evaluator) eval(ctx context.Context, expr parser.Expr) (parser.Value,
 					mat[i].Histograms[j].H = mat[i].Histograms[j].H.Copy().Mul(-1)
 				}
 			}
-			if !ev.enableDelayedNameRemoval && mat.ContainsSameLabelset() {
-				ev.errorf("vector cannot contain metrics with the same labelset")
+			if !ev.enableDelayedNameRemoval {
+				mat = ev.mergeSeriesWithSameLabelset(mat)
 			}
 		}
 		return mat, ws
diff --git a/promql/engine_test.go b/promql/engine_test.go
index 80bb75c945..208ac4f89d 100644
--- a/promql/engine_test.go
+++ b/promql/engine_test.go
@@ -3946,6 +3946,41 @@ eval instant at 1m histogram_fraction(-Inf, 0.7071067811865475, histogram_nan)
     {case="100% NaNs"} 0.0
     {case="20% NaNs"} 0.4
 
+# Test unary negation with non-overlapping series that have different metric names.
+# After negation, the __name__ label is dropped, so series with different names
+# but same other labels should merge if they don't overlap in time.
+clear
+load 20m
+  http_requests{job="api"} 2 _
+  http_errors{job="api"} _ 4
+
+eval instant at 0 -{job="api"}
+  {job="api"} -2
+
+eval instant at 20m -{job="api"}
+  {job="api"} -4
+
+eval range from 0 to 20m step 20m -{job="api"}
+  {job="api"} -2 -4
+
+# Test unary negation failure with overlapping timestamps (same labelset at same time).
+clear
+load 1m
+  http_requests{job="api"} 1
+  http_errors{job="api"} 2
+
+eval_fail instant at 0 -{job="api"}
+
+# Test unary negation with "or" operator combining metrics with removed names.
+clear
+load 10m
+    metric_a   1  _
+    metric_b   3  4
+
+# Use "-" unary operator as a simple way to remove the metric name.
+eval range from 0 to 20m step 10m -metric_a or -metric_b
+    {} -1  -4
+
 `, engine)
 }
 
diff --git a/promql/promqltest/testdata/operators.test b/promql/promqltest/testdata/operators.test
index e570be9630..cd608b3c36 100644
--- a/promql/promqltest/testdata/operators.test
+++ b/promql/promqltest/testdata/operators.test
@@ -980,3 +980,40 @@ eval instant at 10m (testhistogram) and on() (vector(-1) == 1)
 eval range from 0 to 10m step 5m (testhistogram) and on() (vector(-1) == 1)
 
 clear
+
+# Test unary negation with non-overlapping series that have different metric names.
+# After negation, the __name__ label is dropped, so series with different names
+# but same other labels should merge if they don't overlap in time.
+load 20m
+  http_requests{job="api"} 2 _
+  http_errors{job="api"} _ 4
+
+eval instant at 0 -{job="api"}
+  {job="api"} -2
+
+eval instant at 20m -{job="api"}
+  {job="api"} -4
+
+eval range from 0 to 20m step 20m -{job="api"}
+  {job="api"} -2 -4
+
+# Test unary negation failure with overlapping timestamps (same labelset at same time).
+clear
+load 1m
+  http_requests{job="api"} 1
+  http_errors{job="api"} 2
+
+eval_fail instant at 0 -{job="api"}
+
+clear
+
+# Test unary negation with "or" operator combining metrics with removed names.
+load 10m
+    metric_a   1  _
+    metric_b   3  4
+
+# Use "-" unary operator as a simple way to remove the metric name.
+eval range from 0 to 20m step 10m -metric_a or -metric_b
+    {} -1  -4
+
+clear