diff --git a/services/templater.go b/services/templater.go
index 7036615..b17ed00 100644
--- a/services/templater.go
+++ b/services/templater.go
@@ -6,7 +6,6 @@ import (
 	"errors"
 	"html/template"
 	"image/png"
-	"strconv"
 
 	"github.com/boombuler/barcode"
 	"github.com/boombuler/barcode/code128"
@@ -22,22 +21,20 @@ type Templater interface {
 type DefaultTemplater struct {
 }
 
-func idToEan13(id int, prefix string) (string, error) {
-	idStr := strconv.Itoa(id)
-
-	if len(idStr) > 12 {
+func idToEan13(id string, prefix string) (string, error) {
+	if len(id) > 12 {
 		return "", errors.New("id too long")
 	}
 
-	for len(idStr) < 11 {
-		idStr = "0" + idStr
+	for len(id) < 11 {
+		id = "0" + id
 	}
-	idStr = prefix + idStr
+	id = prefix + id
 
-	return idStr, nil
+	return id, nil
 }
 
-func (t *DefaultTemplater) GenerateBarcode(code int, format string, prefix string) (string, error) {
+func (t *DefaultTemplater) GenerateBarcode(code string, format string, prefix string) (string, error) {
 	var generatedCode barcode.Barcode
 	var err error
 
@@ -53,13 +50,13 @@ func (t *DefaultTemplater) GenerateBarcode(code int, format string, prefix strin
 		}
 		break
 	case "code128":
-		generatedCode, err = code128.Encode(prefix + strconv.Itoa(code))
+		generatedCode, err = code128.Encode(prefix + code)
 		if err != nil {
 			return "", err
 		}
 		break
 	case "qr":
-		generatedCode, err = qr.Encode(prefix+strconv.Itoa(code), qr.M, qr.Numeric)
+		generatedCode, err = qr.Encode(prefix+code, qr.M, qr.AlphaNumeric)
 		if err != nil {
 			return "", err
 		}
diff --git a/templates/contract/de.html b/templates/contract/de.html
index f8dc751..07d3878 100644
--- a/templates/contract/de.html
+++ b/templates/contract/de.html
@@ -56,7 +56,7 @@
         </div>
         <div class="column">
           <img style="vertical-align: revert; margin-top: auto; object-fit: cover; max-height: 2cm;"
-            src="data:image/png;base64,{{ barcode .ID $.BarcodeFormat $.BarcodePrefix }}" />
+            src="data:image/png;base64,{{ barcode (printf "%d" .ID) $.BarcodeFormat $.BarcodePrefix }}" />
         </div>
       </div>
       <div class="columns" style="padding-top: 1rem;">
diff --git a/templates/contract/en.html b/templates/contract/en.html
index 4de8397..0c4c59f 100644
--- a/templates/contract/en.html
+++ b/templates/contract/en.html
@@ -55,7 +55,7 @@
         </div>
         <div class="column">
           <img style="vertical-align: revert; margin-top: auto; object-fit: cover; max-height: 2cm;"
-            src="data:image/png;base64,{{ barcode .ID $.BarcodeFormat $.BarcodePrefix }}"/>
+            src="data:image/png;base64,{{ barcode (printf "%d" .ID) $.BarcodeFormat $.BarcodePrefix }}"/>
         </div>
       </div>
       <div class="columns" style="padding-top: 1rem;">