diff --git a/src/__test__/integration.test.ts b/src/__test__/integration.test.ts
index 5f1bf8e..31452f1 100755
--- a/src/__test__/integration.test.ts
+++ b/src/__test__/integration.test.ts
@@ -90,10 +90,10 @@ describe('mmdb lib', () => {
             float: 0,
             int32: 0,
             map: {},
-            uint128: 0,
+            uint128: 0n,
             uint16: 0,
             uint32: 0,
-            uint64: 0,
+            uint64: 0n,
             utf8_string: '',
           },
         },
@@ -116,10 +116,10 @@ describe('section: data', () => {
       float: 1.100000023841858,
       int32: -268435456,
       map: { mapX: { arrayX: [7, 8, 9], utf8_stringX: 'hello' } },
-      uint128: '1329227995784915872903807060280344576',
+      uint128: 1329227995784915872903807060280344576n,
       uint16: 100,
       uint32: 268435456,
-      uint64: '1152921504606846976',
+      uint64: 1152921504606846976n,
       utf8_string: 'unicode! ☯ - ♫',
     });
   });
@@ -134,10 +134,10 @@ describe('section: data', () => {
       float: 0,
       int32: 0,
       map: {},
-      uint128: 0,
+      uint128: 0n,
       uint16: 0,
       uint32: 0,
-      uint64: 0,
+      uint64: 0n,
       utf8_string: '',
     });
   });
@@ -217,10 +217,10 @@ describe('getWithPrefixLength', () => {
         utf8_stringX: 'hello',
       },
     },
-    uint128: '1329227995784915872903807060280344576',
+    uint128: 1329227995784915872903807060280344576n,
     uint16: 0x64,
     uint32: 268435456,
-    uint64: '1152921504606846976',
+    uint64: 1152921504606846976n,
     utf8_string: 'unicode! ☯ - ♫',
   };
   const tests = [
diff --git a/src/decoder.test.ts b/src/decoder.test.ts
index 1da7825..d091808 100644
--- a/src/decoder.test.ts
+++ b/src/decoder.test.ts
@@ -1,6 +1,4 @@
 import { strict as assert } from 'assert';
-import fs from 'fs';
-import path from 'path';
 import Decoder from './decoder';
 
 describe('lib/decoder', () => {
@@ -14,19 +12,6 @@ describe('lib/decoder', () => {
     });
   });
 
-  describe('decodeUint()', () => {
-    it('should return zero for unsupported int size', () => {
-      const decoder: any = new Decoder(
-        fs.readFileSync(
-          path.join(__dirname, '../test/data/test-data/GeoIP2-City-Test.mmdb')
-        ),
-        1
-      );
-
-      assert.strictEqual(decoder.decodeUint(1, 32), 0);
-    });
-  });
-
   describe('decodeArray()', () => {
     const testCases = [
       {
@@ -407,20 +392,17 @@ describe('lib/decoder', () => {
 
   function generateLargeUintCases(
     bits: 64 | 128
-  ): { expected: number | string; input: number[] }[] {
+  ): { expected: bigint; input: number[] }[] {
     const ctrlByte = bits === 64 ? 0x02 : 0x03;
-    const cases: { expected: number | string; input: number[] }[] = [];
-
-    cases.push({ expected: 0, input: [0x00, ctrlByte] });
-    cases.push({ expected: 500, input: [0x02, ctrlByte, 0x01, 0xf4] });
-    cases.push({ expected: 10872, input: [0x02, ctrlByte, 0x2a, 0x78] });
+    const cases = [
+      { expected: 0n, input: [0x00, ctrlByte] },
+      { expected: 500n, input: [0x02, ctrlByte, 0x01, 0xf4] },
+      { expected: 10872n, input: [0x02, ctrlByte, 0x2a, 0x78] },
+    ];
 
     const maxBytes = bits / 8;
     for (let byteCount = 1; byteCount <= maxBytes; byteCount++) {
-      const expectedNum = (1n << BigInt(8 * byteCount)) - 1n;
-      // For some reason we convert big ints to strings in the decoder
-      const expectedValue =
-        byteCount <= 6 ? Number(expectedNum) : expectedNum.toString();
+      const expectedValue = (1n << BigInt(8 * byteCount)) - 1n;
 
       const inputBytes: number[] = Array(byteCount).fill(0xff);
       const input = [byteCount, ctrlByte, ...inputBytes];
@@ -429,7 +411,7 @@ describe('lib/decoder', () => {
     return cases;
   }
 
-  describe('decodeUint() - uint64', () => {
+  describe('decodeBigUint() - uint64', () => {
     const testCases = generateLargeUintCases(64);
 
     for (const tc of testCases) {
@@ -441,7 +423,7 @@ describe('lib/decoder', () => {
     }
   });
 
-  describe('decodeUint() - uint128', () => {
+  describe('decodeBigUint() - uint128', () => {
     const testCases = generateLargeUintCases(128);
 
     for (const tc of testCases) {
diff --git a/src/decoder.ts b/src/decoder.ts
index 0e001a2..5dd71af 100755
--- a/src/decoder.ts
+++ b/src/decoder.ts
@@ -123,9 +123,9 @@ export default class Decoder {
       case DataType.Int32:
         return cursor(this.decodeInt32(offset, size), newOffset);
       case DataType.Uint64:
-        return cursor(this.decodeUint(offset, size), newOffset);
+        return cursor(this.decodeBigUint(offset, size), newOffset);
       case DataType.Uint128:
-        return cursor(this.decodeUint(offset, size), newOffset);
+        return cursor(this.decodeBigUint(offset, size), newOffset);
     }
 
     throw new Error('Unknown type ' + type + ' at offset ' + offset);
@@ -269,32 +269,31 @@ export default class Decoder {
     return this.db.readInt32BE(offset);
   }
 
-  private decodeUint(offset: number, size: number) {
+  private decodeUint(offset: number, size: number): number {
     if (size === 0) {
       return 0;
     }
-    if (size <= 6) {
+    if (size <= 4) {
       return this.db.readUIntBE(offset, size);
     }
-    if (size == 8) {
-      return this.db.readBigUInt64BE(offset).toString();
-    }
-    if (size > 16) {
-      return 0;
-    }
-    return this.decodeBigUint(offset, size);
+
+    throw new Error(`Invalid size for unsigned integer: ${size}`);
   }
 
   private decodeString(offset: number, size: number) {
     return this.db.toString('utf8', offset, offset + size);
   }
 
-  private decodeBigUint(offset: number, size: number) {
+  private decodeBigUint(offset: number, size: number): bigint {
+    if (size > 16) {
+      throw new Error(`Invalid size for big unsigned integer: ${size}`);
+    }
+
     let integer = 0n;
     for (let i = 0; i < size; i++) {
       integer <<= 8n;
       integer |= BigInt(this.db.readUInt8(offset + i));
     }
-    return integer.toString();
+    return integer;
   }
 }
diff --git a/src/metadata.ts b/src/metadata.ts
index ba1bbec..a51fb3b 100755
--- a/src/metadata.ts
+++ b/src/metadata.ts
@@ -42,7 +42,7 @@ export const parseMetadata = (db: Buffer): Metadata => {
   return {
     binaryFormatMajorVersion: metadata.binary_format_major_version,
     binaryFormatMinorVersion: metadata.binary_format_minor_version,
-    buildEpoch: new Date(metadata.build_epoch * 1000),
+    buildEpoch: new Date(Number(metadata.build_epoch) * 1000),
     databaseType: metadata.database_type,
     description: metadata.description,
     ipVersion: metadata.ip_version,