diff --git a/promql/functions.go b/promql/functions.go
index 925ae83ae5..f844bf5ada 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -1859,11 +1859,8 @@ func (ev *evaluator) evalLabelReplace(ctx context.Context, args parser.Expressio
 			}
 		}
 	}
-	if matrix.ContainsSameLabelset() {
-		ev.errorf("vector cannot contain metrics with the same labelset")
-	}
 
-	return matrix, ws
+	return ev.mergeSeriesWithSameLabelset(matrix), ws
 }
 
 // === Vector(s Scalar) (Vector, Annotations) ===
@@ -1913,11 +1910,8 @@ func (ev *evaluator) evalLabelJoin(ctx context.Context, args parser.Expressions)
 			matrix[i].DropName = el.DropName
 		}
 	}
-	if matrix.ContainsSameLabelset() {
-		ev.errorf("vector cannot contain metrics with the same labelset")
-	}
 
-	return matrix, ws
+	return ev.mergeSeriesWithSameLabelset(matrix), ws
 }
 
 // Common code for date related functions.
diff --git a/promql/promqltest/testdata/functions.test b/promql/promqltest/testdata/functions.test
index ba3df76ff6..7bc4bcb624 100644
--- a/promql/promqltest/testdata/functions.test
+++ b/promql/promqltest/testdata/functions.test
@@ -2014,3 +2014,38 @@ eval instant at 0m scalar({type="histogram"})
 # One float in the vector.
 eval instant at 0m scalar({l="x"})
 	1
+
+clear
+load 20m
+  series{label="a", idx="1"} 2 _
+  series{label="a", idx="2"} _ 4
+
+eval instant at 0 label_replace(series, "idx", "replaced", "idx", ".*")
+  series{label="a", idx="replaced"} 2
+
+eval instant at 20m label_replace(series, "idx", "replaced", "idx", ".*")
+  series{label="a", idx="replaced"} 4
+
+eval range from 0 to 20m step 20m label_replace(series, "idx", "replaced", "idx", ".*")
+  series{label="a", idx="replaced"} 2 4
+
+# Test label_join with non-overlapping series.
+eval instant at 0 label_join(series, "idx", ",", "label", "label")
+  series{label="a", idx="a,a"} 2
+
+eval instant at 20m label_join(series, "idx", ",", "label", "label")
+  series{label="a", idx="a,a"} 4
+
+eval range from 0 to 20m step 20m label_join(series, "idx", ",", "label", "label")
+  series{label="a", idx="a,a"} 2 4
+
+# Test label_replace failure with overlapping timestamps (same labelset at same time).
+clear
+load 1m
+  overlap{label="a", idx="1"} 1
+  overlap{label="a", idx="2"} 2
+
+eval_fail instant at 0 label_replace(overlap, "idx", "same", "idx", ".*")
+
+# Test label_join failure with overlapping timestamps (same labelset at same time).
+eval_fail instant at 0 label_join(overlap, "idx", ",", "label", "label")