diff --git a/int10.js b/int10.js
index f572d03..1859bdd 100644
--- a/int10.js
+++ b/int10.js
@@ -13,7 +13,8 @@
 // ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
-let max = 10000000000000; // biggest 10^n integer that can still fit 2^53 when multiplied by 256
+/** Biggest 10^n integer that can still fit 2^53 when multiplied by 256. */
+const max = 10000000000000;
 
 export class Int10 {
     /**
@@ -26,11 +27,13 @@ export class Int10 {
 
     /**
      * Multiply value by m and add c.
-     * @param {number} m - multiplier, must be < =256
-     * @param {number} c - value to add
+     * @param {number} m - multiplier, must be 0<m<=256
+     * @param {number} c - value to add, must be c>=0
      */
     mulAdd(m, c) {
+        // assert(m > 0)
         // assert(m <= 256)
+        // assert(c >= 0)
         let b = this.buf,
             l = b.length,
             i, t;
@@ -71,11 +74,12 @@ export class Int10 {
 
     /**
      * Convert to decimal string representation.
-     * @param {*} base - optional value, only value accepted is 10
+     * @param {number} [base=10] - optional value, only value accepted is 10
+     * @returns {string} The decimal string representation.
      */
-    toString(base) {
-        if ((base || 10) != 10)
-            throw 'only base 10 is supported';
+    toString(base = 10) {
+        if (base != 10)
+            throw new Error('only base 10 is supported');
         let b = this.buf,
             s = b[b.length - 1].toString();
         for (let i = b.length - 2; i >= 0; --i)
@@ -86,6 +90,7 @@ export class Int10 {
     /**
      * Convert to Number value representation.
      * Will probably overflow 2^53 and thus become approximate.
+     * @returns {number} The numeric value.
      */
     valueOf() {
         let b = this.buf,
@@ -97,6 +102,7 @@ export class Int10 {
 
     /**
      * Return value as a simple Number (if it is <= 10000000000000), or return this.
+     * @returns {number | Int10} The simplified value.
      */
     simplify() {
         let b = this.buf;
diff --git a/test.js b/test.js
index ec3c450..cd88878 100755
--- a/test.js
+++ b/test.js
@@ -3,6 +3,7 @@
 import { ASN1, Stream } from './asn1.js';
 import { Hex } from './hex.js';
 import { Base64 } from './base64.js';
+import { Int10 } from './int10.js';
 
 const all = (process.argv[2] == 'all');
 
@@ -190,6 +191,27 @@ tests.push(new Tests(function (t) {
     'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQR\nSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456w==',
 ]));
 
+tests.push(new Tests(function (t) {
+    this.row = (0|this.row) + 1;
+    this.num = this.num || new Int10();
+    this.num.mulAdd(t[0], t[1]);
+    this.checkResult(this.num.toString(), t[2], 'Int10 row ' + this.row);
+}, [
+    [0, 1000000000, '1000000000'],
+    [256, 23, '256000000023'],
+    [256, 23, '65536000005911'],
+    [256, 23, '16777216001513239'],
+    [256, 23, '4294967296387389207'],
+    [256, 23, '1099511627875171637015'],
+    [256, 23, '281474976736043939075863'],
+    [253, 1, '71213169114219116586193340'],
+    [253, 1, '18016931785897436496306915021'],
+    [253, 1, '4558283741832051433565649500314'],
+    [253, 1, '1153245786683509012692109323579443'],
+    [253, 1, '291771184030927780211103658865599080'],
+    [1, 0, '291771184030927780211103658865599080'],
+]));
+
 for (const t of tests)
     t.checkAll();