diff --git a/BitcoinSwiftTests/BitcoinDecodingTests.swift b/BitcoinSwiftTests/BitcoinDecodingTests.swift
index fb37b25..d8dd237 100644
--- a/BitcoinSwiftTests/BitcoinDecodingTests.swift
+++ b/BitcoinSwiftTests/BitcoinDecodingTests.swift
@@ -129,14 +129,16 @@ class BitcoinDecodingTests: XCTestCase {
 
     // Test reading a little-endian UInt64.
     if let int = stream.readUInt64() {
-      XCTAssertEqual(int, UInt64(0x0807060504030201))
+      let varInt:UInt64 = 0x0807060504030201
+      XCTAssertEqual(int, varInt)
     } else {
       XCTFail("Failed to read int")
     }
 
     // Test reading a big-endian UInt64.
     if let int = stream.readUInt64(.BigEndian) {
-      XCTAssertEqual(int, UInt64(0x090a0b0c0d0e0f10))
+      let varInt:UInt64 = 0x090a0b0c0d0e0f10
+      XCTAssertEqual(int, varInt)
     } else {
       XCTFail("Failed to read int")
     }
@@ -362,7 +364,8 @@ class BitcoinDecodingTests: XCTestCase {
     let stream = NSInputStream(data: data)
     stream.open()
     if let uint64 = stream.readVarInt() {
-      XCTAssertEqual(uint64, UInt64(0x0102030405060708))
+      let varInt:UInt64 = 0x0102030405060708
+      XCTAssertEqual(uint64, varInt)
     } else {
       XCTFail("Failed to read varint")
     }
diff --git a/BitcoinSwiftTests/BitcoinEncodingTests.swift b/BitcoinSwiftTests/BitcoinEncodingTests.swift
index 497308e..33d343a 100644
--- a/BitcoinSwiftTests/BitcoinEncodingTests.swift
+++ b/BitcoinSwiftTests/BitcoinEncodingTests.swift
@@ -48,7 +48,8 @@ class BitcoinEncodingTests: XCTestCase {
 
   func testAppendUInt64LittleEndian() {
     let data = NSMutableData()
-    data.appendUInt64(UInt64(0x0102030405060708))
+    let varInt:UInt64 = 0x0102030405060708
+    data.appendUInt64(varInt)
     let expectedData = NSData(bytes: [0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01] as [UInt8],
                               length: 8)
     XCTAssertEqual(data, expectedData)
@@ -56,7 +57,8 @@ class BitcoinEncodingTests: XCTestCase {
 
   func testAppendUInt64BigEndian() {
     let data = NSMutableData()
-    data.appendUInt64(UInt64(0x0102030405060708), endianness: .BigEndian)
+    let varInt:UInt64 = 0x0102030405060708
+    data.appendUInt64(varInt, endianness: .BigEndian)
     let expectedData = NSData(bytes: [0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08] as [UInt8],
                               length: 8)
     XCTAssertEqual(data, expectedData)
@@ -139,7 +141,8 @@ class BitcoinEncodingTests: XCTestCase {
 
   func testAppendVarIntUInt64() {
     let data = NSMutableData()
-    data.appendVarInt(0x0100000000)
+    let varInt:UInt64 = 0x0100000000
+    data.appendVarInt(varInt)
     let expectedData =
         NSData(bytes: [0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00] as [UInt8], length: 9)
     XCTAssertEqual(data, expectedData)