diff --git a/promql/parser/generated_parser.y b/promql/parser/generated_parser.y
index de9234589c..d8fb311154 100644
--- a/promql/parser/generated_parser.y
+++ b/promql/parser/generated_parser.y
@@ -452,7 +452,7 @@ positive_duration_expr : duration_expr
 offset_expr: expr OFFSET duration_expr
                         {
                         if numLit, ok := $3.(*NumberLiteral); ok {
-                            yylex.(*parser).addOffset($1, time.Duration(numLit.Val*1000)*time.Millisecond)
+                            yylex.(*parser).addOffset($1, time.Duration(math.Round(numLit.Val*float64(time.Second))))
                             $$ = $1
                             break
                         }
@@ -506,7 +506,7 @@ matrix_selector : expr LEFT_BRACKET positive_duration_expr RIGHT_BRACKET
 
                         var rangeNl time.Duration
                         if numLit, ok := $3.(*NumberLiteral); ok {
-                                rangeNl = time.Duration(numLit.Val*1000)*time.Millisecond
+                                rangeNl = time.Duration(math.Round(numLit.Val*float64(time.Second)))
                         }
                         rangeExpr, _ := $3.(*DurationExpr)
                         $$ = &MatrixSelector{
@@ -523,11 +523,11 @@ subquery_expr   : expr LEFT_BRACKET positive_duration_expr COLON positive_durati
                         var rangeNl time.Duration
                         var stepNl time.Duration
                         if numLit, ok := $3.(*NumberLiteral); ok {
-                                rangeNl = time.Duration(numLit.Val*1000)*time.Millisecond
+                                rangeNl = time.Duration(math.Round(numLit.Val*float64(time.Second)))
                         }
                         rangeExpr, _ := $3.(*DurationExpr)
                         if numLit, ok := $5.(*NumberLiteral); ok {
-                                stepNl = time.Duration(numLit.Val*1000)*time.Millisecond
+                                stepNl = time.Duration(math.Round(numLit.Val*float64(time.Second)))
                         }
                         stepExpr, _ := $5.(*DurationExpr)
                         $$ = &SubqueryExpr{
@@ -543,7 +543,7 @@ subquery_expr   : expr LEFT_BRACKET positive_duration_expr COLON positive_durati
                         {
                         var rangeNl time.Duration
                         if numLit, ok := $3.(*NumberLiteral); ok {
-                                rangeNl = time.Duration(numLit.Val*1000)*time.Millisecond
+                                rangeNl = time.Duration(math.Round(numLit.Val*float64(time.Second)))
                         }
                         rangeExpr, _ := $3.(*DurationExpr)
                         $$ = &SubqueryExpr{
diff --git a/promql/parser/generated_parser.y.go b/promql/parser/generated_parser.y.go
index 8c84b42f14..7e7ec2dbd3 100644
--- a/promql/parser/generated_parser.y.go
+++ b/promql/parser/generated_parser.y.go
@@ -1372,7 +1372,7 @@ yydefault:
 		yyDollar = yyS[yypt-3 : yypt+1]
 		{
 			if numLit, ok := yyDollar[3].node.(*NumberLiteral); ok {
-				yylex.(*parser).addOffset(yyDollar[1].node, time.Duration(numLit.Val*1000)*time.Millisecond)
+				yylex.(*parser).addOffset(yyDollar[1].node, time.Duration(math.Round(numLit.Val*float64(time.Second))))
 				yyVAL.node = yyDollar[1].node
 				break
 			}
@@ -1423,7 +1423,7 @@ yydefault:
 
 			var rangeNl time.Duration
 			if numLit, ok := yyDollar[3].node.(*NumberLiteral); ok {
-				rangeNl = time.Duration(numLit.Val*1000) * time.Millisecond
+				rangeNl = time.Duration(math.Round(numLit.Val * float64(time.Second)))
 			}
 			rangeExpr, _ := yyDollar[3].node.(*DurationExpr)
 			yyVAL.node = &MatrixSelector{
@@ -1439,11 +1439,11 @@ yydefault:
 			var rangeNl time.Duration
 			var stepNl time.Duration
 			if numLit, ok := yyDollar[3].node.(*NumberLiteral); ok {
-				rangeNl = time.Duration(numLit.Val*1000) * time.Millisecond
+				rangeNl = time.Duration(math.Round(numLit.Val * float64(time.Second)))
 			}
 			rangeExpr, _ := yyDollar[3].node.(*DurationExpr)
 			if numLit, ok := yyDollar[5].node.(*NumberLiteral); ok {
-				stepNl = time.Duration(numLit.Val*1000) * time.Millisecond
+				stepNl = time.Duration(math.Round(numLit.Val * float64(time.Second)))
 			}
 			stepExpr, _ := yyDollar[5].node.(*DurationExpr)
 			yyVAL.node = &SubqueryExpr{
@@ -1460,7 +1460,7 @@ yydefault:
 		{
 			var rangeNl time.Duration
 			if numLit, ok := yyDollar[3].node.(*NumberLiteral); ok {
-				rangeNl = time.Duration(numLit.Val*1000) * time.Millisecond
+				rangeNl = time.Duration(math.Round(numLit.Val * float64(time.Second)))
 			}
 			rangeExpr, _ := yyDollar[3].node.(*DurationExpr)
 			yyVAL.node = &SubqueryExpr{
diff --git a/promql/parser/parse_test.go b/promql/parser/parse_test.go
index a09ccea9d6..2764dc52df 100644
--- a/promql/parser/parse_test.go
+++ b/promql/parser/parse_test.go
@@ -2008,6 +2008,57 @@ var testExpr = []struct {
 		errMsg: `unexpected "}" in label matching, expected string`,
 	},
 	// Test matrix selector.
+	{
+		input: "test[1000ms]",
+		expected: &MatrixSelector{
+			VectorSelector: &VectorSelector{
+				Name: "test",
+				LabelMatchers: []*labels.Matcher{
+					MustLabelMatcher(labels.MatchEqual, model.MetricNameLabel, "test"),
+				},
+				PosRange: posrange.PositionRange{
+					Start: 0,
+					End:   4,
+				},
+			},
+			Range:  1000 * time.Millisecond,
+			EndPos: 12,
+		},
+	},
+	{
+		input: "test[1001ms]",
+		expected: &MatrixSelector{
+			VectorSelector: &VectorSelector{
+				Name: "test",
+				LabelMatchers: []*labels.Matcher{
+					MustLabelMatcher(labels.MatchEqual, model.MetricNameLabel, "test"),
+				},
+				PosRange: posrange.PositionRange{
+					Start: 0,
+					End:   4,
+				},
+			},
+			Range:  1001 * time.Millisecond,
+			EndPos: 12,
+		},
+	},
+	{
+		input: "test[1002ms]",
+		expected: &MatrixSelector{
+			VectorSelector: &VectorSelector{
+				Name: "test",
+				LabelMatchers: []*labels.Matcher{
+					MustLabelMatcher(labels.MatchEqual, model.MetricNameLabel, "test"),
+				},
+				PosRange: posrange.PositionRange{
+					Start: 0,
+					End:   4,
+				},
+			},
+			Range:  1002 * time.Millisecond,
+			EndPos: 12,
+		},
+	},
 	{
 		input: "test[5s]",
 		expected: &MatrixSelector{
diff --git a/promql/promqltest/testdata/functions.test b/promql/promqltest/testdata/functions.test
index fafe2dda40..d37aeb53f6 100644
--- a/promql/promqltest/testdata/functions.test
+++ b/promql/promqltest/testdata/functions.test
@@ -1019,6 +1019,47 @@ eval instant at 1m sum_over_time(metric[2m])
 eval instant at 1m avg_over_time(metric[2m])
   {} 0.5
 
+# Test per-series aggregation on dense samples.
+clear
+load 1ms
+  metric 1+0x4000
+
+eval instant at 4s sum_over_time(metric[1000ms])
+  {} 1000
+
+eval instant at 4s sum_over_time(metric[1001ms])
+  {} 1001
+
+eval instant at 4s sum_over_time(metric[1002ms])
+  {} 1002
+
+eval instant at 4s sum_over_time(metric[1003ms])
+  {} 1003
+
+eval instant at 4s sum_over_time(metric[2000ms])
+  {} 2000
+
+eval instant at 4s sum_over_time(metric[2001ms])
+  {} 2001
+
+eval instant at 4s sum_over_time(metric[2002ms])
+  {} 2002
+
+eval instant at 4s sum_over_time(metric[2003ms])
+  {} 2003
+
+eval instant at 4s sum_over_time(metric[3000ms])
+  {} 3000
+
+eval instant at 4s sum_over_time(metric[3001ms])
+  {} 3001
+
+eval instant at 4s sum_over_time(metric[3002ms])
+  {} 3002
+
+eval instant at 4s sum_over_time(metric[3003ms])
+  {} 3003
+
 # Tests for stddev_over_time and stdvar_over_time.
 clear
 load 10s