diff --git a/arguments.go b/arguments.go
index 61d980c..b17182f 100644
--- a/arguments.go
+++ b/arguments.go
@@ -1,35 +1,57 @@
 package main
 
 import (
+	"fmt"
+	"runtime"
 	"strconv"
 	"time"
 
 	"github.com/docopt/docopt-go"
 )
 
+const maxConcurrency = 256
+
+var defaultConcurrency = func() int {
+	n := 8 * runtime.NumCPU() // 8 is an empirical value.
+
+	if n < maxConcurrency {
+		return n
+	}
+
+	return maxConcurrency
+}()
+
 const usage = `Link checker for Markdown and HTML
 
 Usage:
-	liche [-t <timeout>] [-v] <filenames>...
+	liche [-c <num-requests>] [-t <timeout>] [-v] <filenames>...
 
 Options:
-	-v, --verbose  Be verbose
-	-t, --timeout <timeout>  Set timeout for HTTP requests in seconds [default: 5]`
+	-c, --concurrency <num-requests>  Set max number of concurrent HTTP requests [default: %v]
+	-t, --timeout <timeout>  Set timeout for HTTP requests in seconds [default: 5]
+	-v, --verbose  Be verbose`
 
 type arguments struct {
-	filenames []string
-	timeout   time.Duration
-	verbose   bool
+	filenames   []string
+	concurrency int
+	timeout     time.Duration
+	verbose     bool
 }
 
 func getArgs() (arguments, error) {
-	args, err := docopt.Parse(usage, nil, true, "liche", true)
+	args, err := docopt.Parse(fmt.Sprintf(usage, defaultConcurrency), nil, true, "liche", true)
+
+	if err != nil {
+		return arguments{}, err
+	}
+
+	c, err := strconv.ParseInt(args["--concurrency"].(string), 10, 32)
 
 	if err != nil {
 		return arguments{}, err
 	}
 
-	f, err := strconv.ParseFloat(args["--timeout"].(string), 64)
+	t, err := strconv.ParseFloat(args["--timeout"].(string), 64)
 
 	if err != nil {
 		return arguments{}, err
@@ -37,7 +59,8 @@ func getArgs() (arguments, error) {
 
 	return arguments{
 		args["<filenames>"].([]string),
-		time.Duration(f) * time.Second,
+		int(c),
+		time.Duration(t) * time.Second,
 		args["--verbose"].(bool),
 	}, nil
 }
diff --git a/examples/markdown.feature b/examples/markdown.feature
index 9e546be..8543d09 100644
--- a/examples/markdown.feature
+++ b/examples/markdown.feature
@@ -112,3 +112,11 @@ Feature: Markdown
     """
     When I successfully run `liche --timeout 10 foo.md`
     Then the stdout should contain exactly ""
+
+  Scenario: Set concurrency
+    Given a file named "foo.md" with:
+    """
+    [Google](https://google.com)
+    """
+    When I successfully run `liche --concurrency 10 foo.md`
+    Then the stdout should contain exactly ""
diff --git a/file_checker.go b/file_checker.go
index dcba151..a17359c 100644
--- a/file_checker.go
+++ b/file_checker.go
@@ -15,8 +15,8 @@ type fileChecker struct {
 	urlChecker urlChecker
 }
 
-func newFileChecker(timeout time.Duration) fileChecker {
-	return fileChecker{newURLChecker(timeout)}
+func newFileChecker(timeout time.Duration, s semaphore) fileChecker {
+	return fileChecker{newURLChecker(timeout, s)}
 }
 
 func (c fileChecker) Check(f string) ([]urlResult, error) {
diff --git a/main.go b/main.go
index c1e0ae4..bda8dc2 100644
--- a/main.go
+++ b/main.go
@@ -11,7 +11,8 @@ func main() {
 	}
 
 	rc := make(chan fileResult, len(args.filenames))
-	c := newFileChecker(args.timeout)
+	s := newSemaphore(args.concurrency)
+	c := newFileChecker(args.timeout, s)
 
 	go c.CheckMany(args.filenames, rc)
 
diff --git a/url_checker.go b/url_checker.go
index be880ed..0fabf8c 100644
--- a/url_checker.go
+++ b/url_checker.go
@@ -2,34 +2,22 @@ package main
 
 import (
 	"net/http"
-	"runtime"
 	"sync"
 	"time"
 )
 
-const maxOpenFiles = 512
-
-var sem = make(chan bool, func() int {
-	n := 8 * runtime.NumCPU() // 8 is an empirical value.
-
-	if n < maxOpenFiles {
-		return n
-	}
-
-	return maxOpenFiles
-}())
-
 type urlChecker struct {
-	client http.Client
+	client    http.Client
+	semaphore semaphore
 }
 
-func newURLChecker(timeout time.Duration) urlChecker {
-	return urlChecker{http.Client{Timeout: timeout}}
+func newURLChecker(t time.Duration, s semaphore) urlChecker {
+	return urlChecker{http.Client{Timeout: t}, s}
 }
 
 func (c urlChecker) Check(s string) (resultErr error) {
-	sem <- true
-	defer func() { <-sem }()
+	c.semaphore.Request()
+	defer c.semaphore.Release()
 
 	res, err := c.client.Get(s)