diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ValidRefNameTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ValidRefNameTest.java
index f069b65f6..d431a8910 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ValidRefNameTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ValidRefNameTest.java
@@ -44,6 +44,7 @@
 package org.eclipse.jgit.lib;
 
 import static org.eclipse.jgit.junit.Assert.assertEquals;
+import static org.junit.Assert.assertEquals;
 
 import org.eclipse.jgit.junit.MockSystemReader;
 import org.eclipse.jgit.util.SystemReader;
@@ -94,6 +95,25 @@ public class ValidRefNameTest {
 		}
 	}
 
+	private static void assertNormalized(final String name,
+			final String expected) {
+		SystemReader instance = SystemReader.getInstance();
+		try {
+			setUnixSystemReader();
+			String normalized = Repository.normalizeBranchName(name);
+			assertEquals("Normalization of " + name, expected, normalized);
+			assertEquals("\"" + normalized + "\"", true,
+					Repository.isValidRefName(Constants.R_HEADS + normalized));
+			setWindowsSystemReader();
+			normalized = Repository.normalizeBranchName(name);
+			assertEquals("Normalization of " + name, expected, normalized);
+			assertEquals("\"" + normalized + "\"", true,
+					Repository.isValidRefName(Constants.R_HEADS + normalized));
+		} finally {
+			SystemReader.setInstance(instance);
+		}
+	}
+
 	@Test
 	public void testEmptyString() {
 		assertValid(false, "");
@@ -250,97 +270,56 @@ public class ValidRefNameTest {
 
 	@Test
 	public void testNormalizeBranchName() {
-
+		assertEquals(true, Repository.normalizeBranchName(null) == "");
 		assertEquals(true, Repository.normalizeBranchName("").equals(""));
+		assertNormalized("Bug 12345::::Hello World", "Bug_12345-Hello_World");
+		assertNormalized("Bug 12345 :::: Hello World", "Bug_12345_Hello_World");
+		assertNormalized("Bug 12345 :::: Hello::: World",
+				"Bug_12345_Hello-World");
+		assertNormalized(":::Bug 12345 - Hello World", "Bug_12345_Hello_World");
+		assertNormalized("---Bug 12345 - Hello World", "Bug_12345_Hello_World");
+		assertNormalized("Bug 12345 ---- Hello --- World",
+				"Bug_12345_Hello_World");
+		assertNormalized("Bug 12345 - Hello World!", "Bug_12345_Hello_World!");
+		assertNormalized("Bug 12345 : Hello World!", "Bug_12345_Hello_World!");
+		assertNormalized("Bug 12345 _ Hello World!", "Bug_12345_Hello_World!");
+		assertNormalized("Bug 12345   -       Hello World!",
+				"Bug_12345_Hello_World!");
+		assertNormalized(" Bug 12345   -   Hello World! ",
+				"Bug_12345_Hello_World!");
+		assertNormalized(" Bug 12345   -   Hello World!   ",
+				"Bug_12345_Hello_World!");
+		assertNormalized("Bug 12345   -   Hello______ World!",
+				"Bug_12345_Hello_World!");
+		assertNormalized("_Bug 12345 - Hello World!", "Bug_12345_Hello_World!");
+	}
 
-		assertEquals(true,
-				Repository.normalizeBranchName("__@#$@#$@$____   _")
-						.equals(""));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("~`!@#$%^&*()_+}]{[|\\\";?>.<,/")
-						.equals(""));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 :::: Hello World")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 :::: Hello::: World")
-						.equals("Bug_12345-Hello-_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName(":::Bug 12345 - Hello World")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("---Bug 12345 - Hello World")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 ---- Hello --- World")
-						.equals("Bug_12345-Hello-World"));
-
-		assertEquals(true, Repository.normalizeBranchName(null) == null);
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 - Hello World!")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 : Hello World!")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 12345 _ Hello World!")
-						.equals("Bug_12345_Hello_World"));
-
-		assertEquals(true,
-				Repository
-						.normalizeBranchName("Bug 12345   -       Hello World!")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName(" Bug 12345   -   Hello World! ")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository
-						.normalizeBranchName(" Bug 12345   -   Hello World!   ")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository
-						.normalizeBranchName(
-								"Bug 12345   -   Hello______ World!")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("_Bug 12345 - Hello World!")
-						.equals("Bug_12345-Hello_World"));
-
-		assertEquals(true,
-				Repository
-						.normalizeBranchName(
-								"Bug 12345 - Hello Wo!@#$%^&*(rld {@")
-						.equals("Bug_12345-Hello_World_"));
-
-		assertEquals(true,
-				Repository.normalizeBranchName("Bug 1#$  2345 - Hello World")
-						.equals("Bug_12345-Hello_World"));
+	@Test
+	public void testNormalizeWithSlashes() {
+		assertNormalized("foo/bar/baz", "foo/bar/baz");
+		assertNormalized("foo/bar.lock/baz.lock", "foo/bar_lock/baz_lock");
+		assertNormalized("foo/.git/.git~1/bar", "foo/git/git-1/bar");
+		assertNormalized(".foo/aux/con/com3.txt/com0/prn/lpt1",
+				"foo/+aux/+con/+com3.txt/com0/+prn/+lpt1");
+		assertNormalized("foo/../bar///.--ba...z", "foo/bar/ba.z");
+	}
+
+	@Test
+	public void testNormalizeWithUnicode() {
+		assertNormalized("f\u00f6\u00f6/.b\u00e0r/*[<>|^~/b\u00e9\\z",
+				"f\u00f6\u00f6/b\u00e0r/b\u00e9-z");
+		assertNormalized("\u5165\u53e3 entrance;/.\u51fa\u53e3_*ex*it*/",
+				"\u5165\u53e3_entrance;/\u51fa\u53e3_ex-it");
 	}
 
 	@Test
 	public void testNormalizeAlreadyValidRefName() {
-		assertEquals(true,
-				Repository.normalizeBranchName("refs/heads/m.a.s.t.e.r")
-						.equals("refs/heads/m.a.s.t.e.r"));
+		assertNormalized("refs/heads/m.a.s.t.e.r", "refs/heads/m.a.s.t.e.r");
+		assertNormalized("refs/tags/v1.0-20170223", "refs/tags/v1.0-20170223");
 	}
 
 	@Test
 	public void testNormalizeTrimmedUnicodeAlreadyValidRefName() {
-		assertEquals(true,
-				Repository.normalizeBranchName(" \u00e5ngstr\u00f6m\t")
-						.equals("\u00e5ngstr\u00f6m"));
+		assertNormalized(" \u00e5ngstr\u00f6m\t", "\u00e5ngstr\u00f6m");
 	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
index e2f6c3c71..9b1c2eac7 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
@@ -66,6 +66,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.regex.Pattern;
 
 import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
@@ -111,6 +112,17 @@ public abstract class Repository implements AutoCloseable {
 	private static final Logger LOG = LoggerFactory.getLogger(Repository.class);
 	private static final ListenerList globalListeners = new ListenerList();
 
+	/**
+	 * Branch names containing slashes should not have a name component that is
+	 * one of the reserved device names on Windows.
+	 *
+	 * @see #normalizeBranchName(String)
+	 */
+	private static final Pattern FORBIDDEN_BRANCH_NAME_COMPONENTS = Pattern
+			.compile(
+					"(^|/)(aux|com[1-9]|con|lpt[1-9]|nul|prn)(\\.[^/]*)?", //$NON-NLS-1$
+					Pattern.CASE_INSENSITIVE);
+
 	/** @return the global listener list observing all events in this JVM. */
 	public static ListenerList getGlobalListenerList() {
 		return globalListeners;
@@ -923,7 +935,7 @@ public abstract class Repository implements AutoCloseable {
 		else
 			desc = getClass().getSimpleName() + "-" //$NON-NLS-1$
 					+ System.identityHashCode(this);
-		return "Repository[" + desc + "]"; //$NON-NLS-1$
+		return "Repository[" + desc + "]"; //$NON-NLS-1$ //$NON-NLS-2$
 	}
 
 	/**
@@ -1332,13 +1344,106 @@ public abstract class Repository implements AutoCloseable {
 		return components > 1;
 	}
 
+	/**
+	 * Normalizes the passed branch name into a possible valid branch name. The
+	 * validity of the returned name should be checked by a subsequent call to
+	 * {@link #isValidRefName(String)}.
+	 * <p/>
+	 * Future implementations of this method could be more restrictive or more
+	 * lenient about the validity of specific characters in the returned name.
+	 * <p/>
+	 * The current implementation returns the trimmed input string if this is
+	 * already a valid branch name. Otherwise it returns a trimmed string with
+	 * special characters not allowed by {@link #isValidRefName(String)}
+	 * replaced by hyphens ('-') and blanks replaced by underscores ('_').
+	 * Leading and trailing slashes, dots, hyphens, and underscores are removed.
+	 *
+	 * @param name
+	 *            to normalize
+	 *
+	 * @return The normalized name or an empty String if it is {@code null} or
+	 *         empty.
+	 * @since 4.7
+	 * @see #isValidRefName(String)
+	 */
+	public static String normalizeBranchName(String name) {
+		if (name == null || name.isEmpty()) {
+			return ""; //$NON-NLS-1$
+		}
+		String result = name.trim();
+		String fullName = result.startsWith(Constants.R_HEADS) ? result
+				: Constants.R_HEADS + result;
+		if (isValidRefName(fullName)) {
+			return result;
+		}
+
+		// All Unicode blanks to underscore
+		result = result.replaceAll("(?:\\h|\\v)+", "_"); //$NON-NLS-1$ //$NON-NLS-2$
+		StringBuilder b = new StringBuilder();
+		char p = '/';
+		for (int i = 0, len = result.length(); i < len; i++) {
+			char c = result.charAt(i);
+			if (c < ' ' || c == 127) {
+				continue;
+			}
+			// Substitute a dash for problematic characters
+			switch (c) {
+			case '\\':
+			case '^':
+			case '~':
+			case ':':
+			case '?':
+			case '*':
+			case '[':
+			case '@':
+			case '<':
+			case '>':
+			case '|':
+			case '"':
+				c = '-';
+				break;
+			default:
+				break;
+			}
+			// Collapse multiple slashes, dashes, dots, underscores, and omit
+			// dashes, dots, and underscores following a slash.
+			switch (c) {
+			case '/':
+				if (p == '/') {
+					continue;
+				}
+				p = '/';
+				break;
+			case '.':
+			case '_':
+			case '-':
+				if (p == '/' || p == '-') {
+					continue;
+				}
+				p = '-';
+				break;
+			default:
+				p = c;
+				break;
+			}
+			b.append(c);
+		}
+		// Strip trailing special characters, and avoid the .lock extension
+		result = b.toString().replaceFirst("[/_.-]+$", "") //$NON-NLS-1$ //$NON-NLS-2$
+				.replaceAll("\\.lock($|/)", "_lock$1"); //$NON-NLS-1$ //$NON-NLS-2$
+		return FORBIDDEN_BRANCH_NAME_COMPONENTS.matcher(result)
+				.replaceAll("$1+$2$3"); //$NON-NLS-1$
+	}
+
 	/**
 	 * Strip work dir and return normalized repository path.
 	 *
-	 * @param workDir Work dir
-	 * @param file File whose path shall be stripped of its workdir
-	 * @return normalized repository relative path or the empty
-	 *         string if the file is not relative to the work directory.
+	 * @param workDir
+	 *            Work dir
+	 * @param file
+	 *            File whose path shall be stripped of its workdir
+	 * @return normalized repository relative path or the empty string if the
+	 *         file is not relative to the work directory.
 	 */
 	@NonNull
 	public static String stripWorkDir(File workDir, File file) {
@@ -1889,46 +1994,4 @@ public abstract class Repository implements AutoCloseable {
 	public void autoGC(ProgressMonitor monitor) {
 		// default does nothing
 	}
-
-	/**
-	 * Normalizes the passed branch name into a possible valid branch name. The
-	 * validity of the returned name should be checked by a subsequent call to
-	 * {@link #isValidRefName(String)}.
-	 * <p/>
-	 * Future implementations of this method could be more restrictive or more
-	 * lenient about the validity of specific characters in the returned name.
-	 * <p/>
-	 * The current implementation returns the trimmed input string if this is
-	 * already a valid branch name. Otherwise it returns a trimmed string only
-	 * containing word characters ([a-zA-Z_0-9]) and hyphens ('-'). Colons are
-	 * replaced by hyphens. Repeating underscores and hyphens are replaced by a
-	 * single occurrence. Underscores and hyphens at the beginning of the string
-	 * are removed.
-	 *
-	 * @param name
-	 *            The name to normalize.
-	 *
-	 * @return The normalized String or null if null was passed.
-	 * @since 4.7
-	 * @see #isValidRefName(String)
-	 */
-	public static String normalizeBranchName(String name) {
-		if (name == null || name.length() == 0) {
-			return name;
-		}
-		String result = name.trim();
-		String fullName = result.startsWith(Constants.R_HEADS) ? result
-				: Constants.R_HEADS + result;
-		if (isValidRefName(fullName)) {
-			return result;
-		}
-		return result.replaceAll("\\s+([_:-])*?\\s+", "$1") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll(":", "-") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll("\\s+", "_") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll("_{2,}", "_") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll("-{2,}", "-") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll("[^\\w-]", "") //$NON-NLS-1$ //$NON-NLS-2$
-				.replaceAll("^_+", "") //$NON-NLS-1$//$NON-NLS-2$
-				.replaceAll("^-+", ""); //$NON-NLS-1$//$NON-NLS-2$
-	}
 }