diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FSTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FSTest.java
index 8de7ba6c1..171d80c3d 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FSTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FSTest.java
@@ -19,7 +19,6 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
@@ -182,7 +181,7 @@ public void testReadPipePosixCommandFailure()
 
 		FS.readPipe(fs.userHome(),
 				new String[] { "/bin/sh", "-c", "exit 1" },
-				Charset.defaultCharset().name());
+				SystemReader.getInstance().getDefaultCharset().name());
 	}
 
 	@Test(expected = CommandFailedException.class)
@@ -192,7 +191,7 @@ public void testReadPipeCommandStartFailure()
 
 		FS.readPipe(fs.userHome(),
 				  new String[] { "this-command-does-not-exist" },
-				  Charset.defaultCharset().name());
+				  SystemReader.getInstance().getDefaultCharset().name());
 	}
 
 	@Test
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
index 3acceab09..74762a902 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -440,6 +440,7 @@ lockOnNotHeld=Lock on {0} not held.
 lockStreamClosed=Output to lock on {0} already closed
 lockStreamMultiple=Output to lock on {0} already opened
 logInconsistentFiletimeDiff={}: inconsistent duration from file timestamps on {}, {}: {} > {}, but diff = {}. Aborting measurement at resolution {}.
+logInvalidDefaultCharset=System property "native.encoding" specifies unknown character set: {}
 logLargerFiletimeDiff={}: inconsistent duration from file timestamps on {}, {}: diff = {} > {} (last good value). Aborting measurement.
 logSmallerFiletime={}: got smaller file timestamp on {}, {}: {} < {}. Aborting measurement at resolution {}.
 logXDGConfigHomeInvalid=Environment variable XDG_CONFIG_HOME contains an invalid path {}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
index ce3ad2239..dbfd41594 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
@@ -12,13 +12,13 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.nio.charset.Charset;
 import java.util.concurrent.Callable;
 
 import org.eclipse.jgit.api.errors.AbortedByHookException;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.ProcessResult;
+import org.eclipse.jgit.util.SystemReader;
 import org.eclipse.jgit.util.io.TeeOutputStream;
 
 /**
@@ -171,7 +171,8 @@ protected void doRun() throws AbortedByHookException, IOException {
 				getStdinArgs());
 		if (result.isExecutedWithError()) {
 			handleError(new String(errorByteArray.toByteArray(),
-					Charset.defaultCharset().name()), result);
+					SystemReader.getInstance().getDefaultCharset().name()),
+					result);
 		}
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
index 76340dabb..3d5d0607e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -468,6 +468,7 @@ public static JGitText get() {
 	/***/ public String lockStreamClosed;
 	/***/ public String lockStreamMultiple;
 	/***/ public String logInconsistentFiletimeDiff;
+	/***/ public String logInvalidDefaultCharset;
 	/***/ public String logLargerFiletimeDiff;
 	/***/ public String logSmallerFiletime;
 	/***/ public String logXDGConfigHomeInvalid;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
index 31a05933c..dd656e5f2 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
@@ -23,7 +23,6 @@
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.Writer;
-import java.nio.charset.Charset;
 import java.nio.file.AccessDeniedException;
 import java.nio.file.FileStore;
 import java.nio.file.Files;
@@ -1507,7 +1506,7 @@ protected File discoverGitSystemConfig() {
 		try {
 			v = readPipe(gitExe.getParentFile(),
 					new String[] { gitExe.getPath(), "--version" }, //$NON-NLS-1$
-				Charset.defaultCharset().name());
+					SystemReader.getInstance().getDefaultCharset().name());
 		} catch (CommandFailedException e) {
 			LOG.warn(e.getMessage());
 			return null;
@@ -1527,7 +1526,7 @@ protected File discoverGitSystemConfig() {
 			w = readPipe(gitExe.getParentFile(),
 					new String[] { gitExe.getPath(), "config", "--system", //$NON-NLS-1$ //$NON-NLS-2$
 							"--edit" }, //$NON-NLS-1$
-				Charset.defaultCharset().name(), env);
+					SystemReader.getInstance().getDefaultCharset().name(), env);
 		} catch (CommandFailedException e) {
 			LOG.warn(e.getMessage());
 			return null;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
index 946d81c73..1c113617f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
@@ -17,7 +17,6 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
-import java.nio.charset.Charset;
 import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.FileStore;
 import java.nio.file.FileSystemException;
@@ -119,8 +118,8 @@ private static int readUmask() {
 					new String[] { "sh", "-c", "umask" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 					null, null);
 			try (BufferedReader lineRead = new BufferedReader(
-					new InputStreamReader(p.getInputStream(), Charset
-							.defaultCharset().name()))) {
+					new InputStreamReader(p.getInputStream(), SystemReader
+							.getInstance().getDefaultCharset().name()))) {
 				if (p.waitFor() == 0) {
 					String s = lineRead.readLine();
 					if (s != null && s.matches("0?\\d{3}")) { //$NON-NLS-1$
@@ -150,7 +149,8 @@ protected File discoverGitExe() {
 					try {
 						String w = readPipe(userHome(),
 							new String[]{"bash", "--login", "-c", "which git"}, // //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$
-							Charset.defaultCharset().name());
+								SystemReader.getInstance().getDefaultCharset()
+										.name());
 						if (!StringUtils.isEmptyOrNull(w)) {
 							gitExe = new File(w);
 						}
@@ -168,7 +168,8 @@ protected File discoverGitExe() {
 				try {
 					String w = readPipe(userHome(),
 							new String[] { "xcode-select", "-p" }, //$NON-NLS-1$ //$NON-NLS-2$
-							Charset.defaultCharset().name());
+							SystemReader.getInstance().getDefaultCharset()
+									.name());
 					if (StringUtils.isEmptyOrNull(w)) {
 						gitExe = null;
 					} else {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java
index d44dc32d1..ff094f697 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java
@@ -13,7 +13,6 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.charset.Charset;
 import java.nio.file.FileVisitOption;
 import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
@@ -150,8 +149,10 @@ protected File discoverGitExe() {
 				String w;
 				try {
 					w = readPipe(userHome(),
-						new String[]{"bash", "--login", "-c", "which git"}, // //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$
-						Charset.defaultCharset().name());
+							new String[] { "bash", "--login", "-c", //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+									"which git" }, // //$NON-NLS-1$
+							SystemReader.getInstance().getDefaultCharset()
+									.name());
 				} catch (CommandFailedException e) {
 					LOG.warn(e.getMessage());
 					return null;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/RawParseUtils.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/RawParseUtils.java
index df9c6c78f..93bf84719 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/RawParseUtils.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/RawParseUtils.java
@@ -1160,7 +1160,7 @@ public static String decodeNoFallback(final Charset cs,
 
 		// Try the default character set. A small group of people
 		// might actually use the same (or very similar) locale.
-		Charset defcs = Charset.defaultCharset();
+		Charset defcs = SystemReader.getInstance().getDefaultCharset();
 		if (!defcs.equals(cs) && !defcs.equals(UTF_8)) {
 			try {
 				return decode(b, defcs);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
index 54fd539f6..16e257791 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
@@ -17,6 +17,9 @@
 import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.nio.charset.Charset;
+import java.nio.charset.IllegalCharsetNameException;
+import java.nio.charset.UnsupportedCharsetException;
 import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -198,6 +201,8 @@ public static void setInstance(SystemReader newReader) {
 
 	private AtomicReference<FileBasedConfig> jgitConfig = new AtomicReference<>();
 
+	private volatile Charset defaultCharset;
+
 	private void init() {
 		// Creating ObjectChecker must be deferred. Unit tests change
 		// behavior of is{Windows,MacOS} in constructor of subclass.
@@ -438,6 +443,35 @@ public Locale getLocale() {
 		return Locale.getDefault();
 	}
 
+	/**
+	 * Retrieves the default {@link Charset} depending on the system locale.
+	 *
+	 * @return the {@link Charset}
+	 * @since 6.0
+	 * @see <a href="https://openjdk.java.net/jeps/400">JEP 400</a>
+	 */
+	public Charset getDefaultCharset() {
+		Charset result = defaultCharset;
+		if (result == null) {
+			// JEP 400: Java 18 populates this system property.
+			String encoding = getProperty("native.encoding"); //$NON-NLS-1$
+			try {
+				if (!StringUtils.isEmptyOrNull(encoding)) {
+					result = Charset.forName(encoding);
+				}
+			} catch (IllegalCharsetNameException
+					| UnsupportedCharsetException e) {
+				LOG.error(JGitText.get().logInvalidDefaultCharset, encoding);
+			}
+			if (result == null) {
+				// This is always UTF-8 on Java >= 18.
+				result = Charset.defaultCharset();
+			}
+			defaultCharset = result;
+		}
+		return result;
+	}
+
 	/**
 	 * Returns a simple date format instance as specified by the given pattern.
 	 *