diff --git a/caddyhttp/fastcgi/fastcgi.go b/caddyhttp/fastcgi/fastcgi.go
index ed051efa..b4aeddd1 100644
--- a/caddyhttp/fastcgi/fastcgi.go
+++ b/caddyhttp/fastcgi/fastcgi.go
@@ -91,7 +91,14 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error)
 			fcgiBackend.SetSendTimeout(rule.SendTimeout)
 
 			var resp *http.Response
-			contentLength, _ := strconv.Atoi(r.Header.Get("Content-Length"))
+
+			var contentLength int64
+			// if ContentLength is already set
+			if r.ContentLength > 0 {
+				contentLength = r.ContentLength
+			} else {
+				contentLength, _ = strconv.ParseInt(r.Header.Get("Content-Length"), 10, 64)
+			}
 			switch r.Method {
 			case "HEAD":
 				resp, err = fcgiBackend.Head(env)
diff --git a/caddyhttp/fastcgi/fcgiclient.go b/caddyhttp/fastcgi/fcgiclient.go
index d7db291c..976e295c 100644
--- a/caddyhttp/fastcgi/fcgiclient.go
+++ b/caddyhttp/fastcgi/fcgiclient.go
@@ -112,7 +112,7 @@ type Client interface {
 	Get(pair map[string]string) (response *http.Response, err error)
 	Head(pair map[string]string) (response *http.Response, err error)
 	Options(pairs map[string]string) (response *http.Response, err error)
-	Post(pairs map[string]string, method string, bodyType string, body io.Reader, contentLength int) (response *http.Response, err error)
+	Post(pairs map[string]string, method string, bodyType string, body io.Reader, contentLength int64) (response *http.Response, err error)
 	Close() error
 	StdErr() bytes.Buffer
 	SetReadTimeout(time.Duration) error
@@ -493,7 +493,7 @@ func (c *FCGIClient) Options(p map[string]string) (resp *http.Response, err erro
 
 // Post issues a POST request to the fcgi responder. with request body
 // in the format that bodyType specified
-func (c *FCGIClient) Post(p map[string]string, method string, bodyType string, body io.Reader, l int) (resp *http.Response, err error) {
+func (c *FCGIClient) Post(p map[string]string, method string, bodyType string, body io.Reader, l int64) (resp *http.Response, err error) {
 	if p == nil {
 		p = make(map[string]string)
 	}
@@ -504,7 +504,7 @@ func (c *FCGIClient) Post(p map[string]string, method string, bodyType string, b
 		p["REQUEST_METHOD"] = "POST"
 	}
 
-	p["CONTENT_LENGTH"] = strconv.Itoa(l)
+	p["CONTENT_LENGTH"] = strconv.FormatInt(l, 10)
 	if len(bodyType) > 0 {
 		p["CONTENT_TYPE"] = bodyType
 	} else {
@@ -518,7 +518,7 @@ func (c *FCGIClient) Post(p map[string]string, method string, bodyType string, b
 // as a string key to a list values (url.Values)
 func (c *FCGIClient) PostForm(p map[string]string, data url.Values) (resp *http.Response, err error) {
 	body := bytes.NewReader([]byte(data.Encode()))
-	return c.Post(p, "POST", "application/x-www-form-urlencoded", body, body.Len())
+	return c.Post(p, "POST", "application/x-www-form-urlencoded", body, int64(body.Len()))
 }
 
 // PostFile issues a POST to the fcgi responder in multipart(RFC 2046) standard,
@@ -560,7 +560,7 @@ func (c *FCGIClient) PostFile(p map[string]string, data url.Values, file map[str
 		return
 	}
 
-	return c.Post(p, "POST", bodyType, buf, buf.Len())
+	return c.Post(p, "POST", bodyType, buf, int64(buf.Len()))
 }
 
 // SetReadTimeout sets the read timeout for future calls that read from the
diff --git a/caddyhttp/fastcgi/fcgiclient_test.go b/caddyhttp/fastcgi/fcgiclient_test.go
index 59879332..f17b8b80 100644
--- a/caddyhttp/fastcgi/fcgiclient_test.go
+++ b/caddyhttp/fastcgi/fcgiclient_test.go
@@ -117,7 +117,7 @@ func sendFcgi(reqType int, fcgiParams map[string]string, data []byte, posts map[
 		if len(data) > 0 {
 			length = len(data)
 			rd := bytes.NewReader(data)
-			resp, err = fcgi.Post(fcgiParams, "", "", rd, rd.Len())
+			resp, err = fcgi.Post(fcgiParams, "", "", rd, int64(rd.Len()))
 		} else if len(posts) > 0 {
 			values := url.Values{}
 			for k, v := range posts {