diff --git a/src/numbers/numbers.go b/src/numbers/numbers.go
index 90d2c80..c82c9c4 100644
--- a/src/numbers/numbers.go
+++ b/src/numbers/numbers.go
@@ -2,8 +2,8 @@ package main
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
-	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -50,12 +50,8 @@ func main() {
 // If all URLs take too long to load or return garbage, an empty JSON list
 // is returned.
 func numbersHandler(w http.ResponseWriter, r *http.Request) {
-	// timeout channel for the handler as a whole
-	timeout := make(chan bool, 1)
-	go func() {
-		time.Sleep(MaxResponseTime)
-		timeout <- true
-	}()
+	ctx, cancel := context.WithTimeout(context.Background(), MaxResponseTime)
+	defer cancel()
 
 	var rurl []string = r.URL.Query()["u"]
 	// if no parameters, return 400
@@ -76,7 +72,7 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 		wg.Add(1)
 		go func(url string) {
 			defer wg.Done()
-			n, e := getNumbers(url)
+			n, e := getNumbers(url, ctx)
 
 			if e == nil {
 				if n != nil && len(n) > 0 {
@@ -109,7 +105,7 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 	done := false
 	for done != true {
 		select {
-		case <-timeout:
+		case <-ctx.Done():
 			log.Printf("Waiting for URL took too long, finishing response anyway")
 			finishResponse(w, sortedNumbers)
 			return
@@ -134,7 +130,7 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 		// sort fallthrough, either the inputChan is currently "empty"
 		// or we fetched all URLs already
 		go func(n []int) {
-			res, err := sort.SortedAndDedup(timeout, n)
+			res, err := sort.SortedAndDedup(ctx, n)
 			if err != nil {
 				return
 			}
@@ -145,7 +141,7 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 		select {
 		case merged := <-sortChan:
 			sortedNumbers = merged
-		case <-timeout:
+		case <-ctx.Done():
 			log.Printf("Sorting took too long, finishing response anyway")
 			finishResponse(w, sortedNumbers)
 			return
@@ -168,7 +164,7 @@ func finishResponse(w http.ResponseWriter, numbers []int) {
 // 'resp' is always nil if there was an error. Errors can
 // be url parse errors, HTTP response errors, io errors from reading the
 // body or json decoding errors.
-func getNumbers(rawurl string) (resp []int, err error) {
+func getNumbers(rawurl string, ctx context.Context) (resp []int, err error) {
 	// validate url
 	u_err := validateURL(rawurl)
 	if u_err != nil {
@@ -176,10 +172,18 @@ func getNumbers(rawurl string) (resp []int, err error) {
 	}
 
 	// retrieve response
-	r, r_err := http.Get(rawurl)
+	client := &http.Client{}
+	req, r_err := http.NewRequest("GET", rawurl, nil)
 	if r_err != nil {
 		return nil, r_err
 	}
+	req = req.WithContext(ctx)
+	r, err := client.Do(req)
+
+	if err != nil {
+		return nil, err
+	}
+
 	if r.StatusCode != 200 {
 		return nil, fmt.Errorf("HTTP: Status code is not 200, but %d",
 			r.StatusCode)
diff --git a/src/numbers/sort/sort.go b/src/numbers/sort/sort.go
index da90cb2..6c35248 100644
--- a/src/numbers/sort/sort.go
+++ b/src/numbers/sort/sort.go
@@ -2,12 +2,13 @@
 package sort
 
 import (
+	"context"
 	"fmt"
 )
 
 // Mergesorts and deduplicates the list.
-func SortedAndDedup(timeout <-chan bool, list []int) (res []int, err error) {
-	sorted, err := Mergesort(timeout, list)
+func SortedAndDedup(ctx context.Context, list []int) (res []int, err error) {
+	sorted, err := Mergesort(ctx, list)
 	if err != nil {
 		return nil, err
 	}
@@ -39,7 +40,7 @@ func dedupSortedList(list []int) []int {
 // is not modified.
 // The algorithm is a bottom-up iterative version and not explained
 // in detail here.
-func Mergesort(timeout <-chan bool, list []int) (res []int, err error) {
+func Mergesort(ctx context.Context, list []int) (res []int, err error) {
 	newList := append([]int{}, list...)
 	temp := append([]int{}, list...)
 	n := len(newList)
@@ -47,7 +48,7 @@ func Mergesort(timeout <-chan bool, list []int) (res []int, err error) {
 	for m := 1; m < (n - 1); m = 2 * m {
 		for i := 0; i < (n - 1); i += 2 * m {
 			select {
-			case <-timeout:
+			case <-ctx.Done():
 				return nil, fmt.Errorf("Sorting timed out")
 			default:
 			}
@@ -55,7 +56,7 @@ func Mergesort(timeout <-chan bool, list []int) (res []int, err error) {
 			mid := i + m - 1
 			to := min(i+2*m-1, n-1)
 
-			merge(timeout, newList, temp, from, mid, to)
+			merge(ctx, newList, temp, from, mid, to)
 		}
 	}
 
@@ -63,7 +64,7 @@ func Mergesort(timeout <-chan bool, list []int) (res []int, err error) {
 }
 
 // The merge part of the mergesort.
-func merge(timeout <-chan bool, list []int, temp []int, from int, mid int, to int) {
+func merge(ctx context.Context, list []int, temp []int, from int, mid int, to int) {
 	k := from
 	i := from
 	j := mid + 1
diff --git a/src/numbers/sort/sort_test.go b/src/numbers/sort/sort_test.go
index 7ce4092..32595fd 100644
--- a/src/numbers/sort/sort_test.go
+++ b/src/numbers/sort/sort_test.go
@@ -1,11 +1,15 @@
 package sort
 
 import (
+	"context"
 	"testing"
 )
 
 // Test the mergesort and deduplication with a predefined set of slices.
 func TestSortAndDedup(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
 	to_sort := [][]int{
 		{},
 		{7},
@@ -29,7 +33,7 @@ func TestSortAndDedup(t *testing.T) {
 	}
 
 	for i := range to_sort {
-		sorted, _ := SortedAndDedup(make(chan bool, 1), to_sort[i])
+		sorted, _ := SortedAndDedup(ctx, to_sort[i])
 		if slice_equal(sorted, result[i]) != true {
 			t.Errorf("Failure in sorting + dedup, expected %s got %s", result[i], sorted)
 		}
@@ -39,6 +43,9 @@ func TestSortAndDedup(t *testing.T) {
 
 // Test the mergesort with a predefined set of slices.
 func TestSort(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
 	// ok
 	to_sort := [][]int{
 		{},
@@ -61,7 +68,7 @@ func TestSort(t *testing.T) {
 	}
 
 	for i := range to_sort {
-		sorted, _ := Mergesort(make(chan bool, 1), to_sort[i])
+		sorted, _ := Mergesort(ctx, to_sort[i])
 		if slice_equal(sorted, result[i]) != true {
 			t.Errorf("Failure in sorting, expected %s got %s", result[i], sorted)
 		}