diff --git a/implementations/javascript/package.json b/implementations/javascript/package.json
index d1c7af7..c6f3aa6 100644
--- a/implementations/javascript/package.json
+++ b/implementations/javascript/package.json
@@ -1,6 +1,6 @@
 {
   "name": "preserves",
-  "version": "0.6.0",
+  "version": "0.6.1",
   "description": "Experimental data serialization format",
   "homepage": "https://gitlab.com/preserves/preserves",
   "license": "Apache-2.0",
diff --git a/implementations/javascript/src/codec.ts b/implementations/javascript/src/codec.ts
index d7be394..d69e478 100644
--- a/implementations/javascript/src/codec.ts
+++ b/implementations/javascript/src/codec.ts
@@ -128,7 +128,7 @@ export class Decoder<T extends object> {
         if (n === 0) return 0;
         let acc = this.nextbyte();
         if (acc & 0x80) acc -= 256;
-        for (let i = 1; i < n; i++) acc = (acc << 8) | this.nextbyte();
+        for (let i = 1; i < n; i++) acc = (acc * 256) + this.nextbyte();
         return acc;
     }
 
@@ -311,7 +311,7 @@ export class Encoder<T extends object> {
 
     encodeint(v: number) {
         // TODO: Bignums :-/
-        const plain_bitcount = Math.floor(Math.log2(v > 0 ? v : ~v)) + 1;
+        const plain_bitcount = Math.floor(Math.log2(v > 0 ? v : -(1 + v))) + 1;
         const signed_bitcount = plain_bitcount + 1;
         const bytecount = (signed_bitcount + 7) >> 3;
         if (bytecount <= 16) {
@@ -322,7 +322,7 @@ export class Encoder<T extends object> {
         }
         const enc = (n: number, x: number) => {
             if (n > 0) {
-                enc(n - 1, x >> 8);
+                enc(n - 1, Math.floor(x / 256));
                 this.emitbyte(x & 255);
             }
         };
diff --git a/tests/samples.bin b/tests/samples.bin
index a832fc3..dba2dcb 100644
Binary files a/tests/samples.bin and b/tests/samples.bin differ
diff --git a/tests/samples.txt b/tests/samples.txt
index a7c21c5..e6450b8 100644
--- a/tests/samples.txt
+++ b/tests/samples.txt
@@ -101,6 +101,7 @@
   int65535: <Test #x"a200ffff" 65535>
   int65536: <Test #x"a2010000" 65536>
   int131072: <Test #x"a2020000" 131072>
+  int2500000000: <Test #x"a4009502f900" 2500000000>
   list0: <Test #x"b584" []>
   list4: <Test #x"b59192939484" [1 2 3 4]>
   list4a: <Test #x"b59192939484" [1, 2, 3, 4]>