diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFile.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFile.java
index c167722dca..e86ab49755 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFile.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFile.java
@@ -108,7 +108,7 @@ public class JarFile extends java.util.jar.JarFile {
 
 	private JarFile(RandomAccessDataFile rootFile, String pathFromRoot,
 			RandomAccessData data, JarEntryFilter filter, JarFileType type)
-			throws IOException {
+					throws IOException {
 		super(rootFile.getFile());
 		this.rootFile = rootFile;
 		this.pathFromRoot = pathFromRoot;
@@ -289,7 +289,7 @@ public class JarFile extends java.util.jar.JarFile {
 
 	@Override
 	public int size() {
-		return (int) this.data.getSize();
+		return this.entries.getSize();
 	}
 
 	@Override
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFileEntries.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFileEntries.java
index f402dff0c3..5f14ac91ef 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFileEntries.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFileEntries.java
@@ -120,6 +120,10 @@ class JarFileEntries implements CentralDirectoryVisitor, Iterable<JarEntry> {
 		}
 	}
 
+	int getSize() {
+		return this.size;
+	}
+
 	private void sort(int left, int right) {
 		// Quick sort algorithm, uses hashCodes as the source but sorts all arrays
 		if (left < right) {
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarFileTests.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarFileTests.java
index c8b6663c5d..4aed20f802 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarFileTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarFileTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
 import java.util.jar.Manifest;
 import java.util.zip.ZipEntry;
+import java.util.zip.ZipFile;
 
 import org.junit.Before;
 import org.junit.Rule;
@@ -168,8 +169,10 @@ public class JarFileTests {
 	}
 
 	@Test
-	public void getSize() {
-		assertThat(this.jarFile.size()).isEqualTo((int) this.rootJarFile.length());
+	public void getSize() throws Exception {
+		try (ZipFile zip = new ZipFile(this.rootJarFile)) {
+			assertThat(this.jarFile.size()).isEqualTo(zip.size());
+		}
 	}
 
 	@Test