diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java
index 96e36a2a6..1a38a7deb 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java
@@ -56,6 +56,7 @@
 import java.util.Collection;
 import java.util.List;
 
+import org.eclipse.jgit.errors.AmbiguousObjectException;
 import org.eclipse.jgit.junit.LocalDiskRepositoryTestCase;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.AbbreviatedObjectId;
@@ -176,13 +177,25 @@ public void testAbbreviateIsActuallyUnique() throws Exception {
 
 		assertEquals(id.abbreviate(20), reader.abbreviate(id, 2));
 
-		Collection<ObjectId> matches = reader.resolve(id.abbreviate(8));
+		AbbreviatedObjectId abbrev8 = id.abbreviate(8);
+		Collection<ObjectId> matches = reader.resolve(abbrev8);
 		assertNotNull(matches);
 		assertEquals(objects.size(), matches.size());
 		for (PackedObjectInfo info : objects)
 			assertTrue("contains " + info.name(), matches.contains(info));
 
-		assertNull("cannot resolve", db.resolve(id.abbreviate(8).name()));
+		try {
+			db.resolve(abbrev8.name());
+			fail("did not throw AmbiguousObjectException");
+		} catch (AmbiguousObjectException err) {
+			assertEquals(abbrev8, err.getAbbreviatedObjectId());
+			matches = err.getCandidates();
+			assertNotNull(matches);
+			assertEquals(objects.size(), matches.size());
+			for (PackedObjectInfo info : objects)
+				assertTrue("contains " + info.name(), matches.contains(info));
+		}
+
 		assertEquals(id, db.resolve(id.abbreviate(20).name()));
 	}
 
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 b62f62b34..078b293f4 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
@@ -63,6 +63,7 @@
 
 import org.eclipse.jgit.JGitText;
 import org.eclipse.jgit.dircache.DirCache;
+import org.eclipse.jgit.errors.AmbiguousObjectException;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
@@ -393,10 +394,15 @@ public RefRename renameRef(final String fromRef, final String toRef) throws IOEx
 	 * @param revstr
 	 *            A git object references expression
 	 * @return an ObjectId or null if revstr can't be resolved to any ObjectId
+	 * @throws AmbiguousObjectException
+	 *             {@code revstr} contains an abbreviated ObjectId and this
+	 *             repository contains more than one object which match to the
+	 *             input abbreviation.
 	 * @throws IOException
 	 *             on serious errors
 	 */
-	public ObjectId resolve(final String revstr) throws IOException {
+	public ObjectId resolve(final String revstr)
+			throws AmbiguousObjectException, IOException {
 		RevWalk rw = new RevWalk(this);
 		try {
 			return resolve(rw, revstr);
@@ -584,6 +590,8 @@ private ObjectId resolveSimple(final String revstr) throws IOException {
 				Collection<ObjectId> matches = reader.resolve(id);
 				if (matches.size() == 1)
 					return matches.iterator().next();
+				if (1 < matches.size())
+					throw new AmbiguousObjectException(id, matches);
 			} finally {
 				reader.release();
 			}