diff --git a/day5/day5.go b/day5/day5.go
index 5f9762a..6c42478 100644
--- a/day5/day5.go
+++ b/day5/day5.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"strings"
+	"sync"
 
 	"gitea.paas.celticinfo.fr/oabrivard/aoc2023/utils"
 )
@@ -38,7 +39,7 @@ func buildMapList(start int, lines []string) ([]*SrcToDest, int) {
 
 func srcToDest(src int64, stdList []*SrcToDest) int64 {
 	for _, std := range stdList {
-		if std.src <= src && src <= std.src+std.rng {
+		if std.src <= src && src <= std.src+std.rng-1 {
 			return src + std.dst - std.src
 		}
 	}
@@ -87,25 +88,43 @@ func FindRangedClosestLocation(lines []string) int64 {
 	tempToHumid, i := buildMapList(i, lines)
 	humidToLoc, _ := buildMapList(i, lines)
 
-	result := int64(math.MaxInt64)
+	var wg sync.WaitGroup
+	ch := make(chan int64, len(seeds)/2)
 
-	count := 0
 	for i := 0; i < len(seeds); i += 2 {
-		count++
-		for seed := seeds[i]; seed < seeds[i]+seeds[i+1]; seed++ {
-			d1 := srcToDest(seed, seedToSoil)
-			d2 := srcToDest(d1, soilToFert)
-			d3 := srcToDest(d2, fertToWater)
-			d4 := srcToDest(d3, waterToLight)
-			d5 := srcToDest(d4, lightToTemp)
-			d6 := srcToDest(d5, tempToHumid)
-			d7 := srcToDest(d6, humidToLoc)
-
-			if d7 < result {
-				result = d7
+		wg.Add(1)
+
+		go func(s int64, r int64) {
+			defer wg.Done()
+			result := int64(math.MaxInt64)
+
+			for seed := s; seed < s+r; seed++ {
+				d1 := srcToDest(seed, seedToSoil)
+				d2 := srcToDest(d1, soilToFert)
+				d3 := srcToDest(d2, fertToWater)
+				d4 := srcToDest(d3, waterToLight)
+				d5 := srcToDest(d4, lightToTemp)
+				d6 := srcToDest(d5, tempToHumid)
+				d7 := srcToDest(d6, humidToLoc)
+
+				if d7 < result {
+					result = d7
+				}
 			}
+
+			fmt.Println("seed roots done:", result)
+			ch <- result
+		}(seeds[i], seeds[i+1])
+	}
+	wg.Wait()
+	close(ch)
+
+	result := int64(math.MaxInt64)
+	for i := range ch {
+		if i < result {
+			result = i
 		}
-		fmt.Println("seed roots done:", count)
 	}
+
 	return result
 }
diff --git a/day5/day5_test.go b/day5/day5_test.go
index 235e49f..76dd3c1 100644
--- a/day5/day5_test.go
+++ b/day5/day5_test.go
@@ -109,7 +109,7 @@ func TestRangedFindClosestLocationWithInput(t *testing.T) {
 	lines := utils.ReadLines("input.txt")
 	result := FindRangedClosestLocation(lines)
 
-	if result != 1181555926 {
-		t.Fatalf("expected 37806487, got %d", result)
+	if result != 37806486 {
+		t.Fatalf("expected 37806486, got %d", result)
 	}
 }