diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/RefListTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/RefListTest.java
index d124d7365..9981bd651 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/RefListTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/RefListTest.java
@@ -127,6 +127,41 @@ public void testBuilder_AddThenSort() {
 		assertSame(REF_B, list.get(1));
 	}
 
+	@Test
+	public void testBuilder_AddThenDedupe() {
+		RefList.Builder<Ref> builder = new RefList.Builder<>(1);
+		builder.add(REF_B);
+		builder.add(REF_A);
+		builder.add(REF_A);
+		builder.add(REF_B);
+		builder.add(REF_c);
+
+		builder.sort();
+		builder.dedupe((a, b) -> b);
+		RefList<Ref> list = builder.toRefList();
+
+		assertEquals(3, list.size());
+		assertSame(REF_A, list.get(0));
+		assertSame(REF_B, list.get(1));
+		assertSame(REF_c, list.get(2));
+	}
+
+	@Test
+	public void testBuilder_AddThenDedupe_Border() {
+		RefList.Builder<Ref> builder = new RefList.Builder<>(1);
+		builder.sort();
+		builder.dedupe((a, b) -> b);
+		RefList<Ref> list = builder.toRefList();
+		assertTrue(list.isEmpty());
+
+		builder = new RefList.Builder<>(1);
+		builder.add(REF_A);
+		builder.sort();
+		builder.dedupe((a, b) -> b);
+		list = builder.toRefList();
+		assertEquals(1, list.size());
+	}
+
 	@Test
 	public void testBuilder_AddAll() {
 		RefList.Builder<Ref> builder = new RefList.Builder<>(1);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
index fe3e8141f..dce06d305 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
@@ -44,8 +44,7 @@
 package org.eclipse.jgit.transport;
 
 import static java.util.Collections.unmodifiableMap;
-import static java.util.function.Function.identity;
-import static java.util.stream.Collectors.toMap;
+import static org.eclipse.jgit.util.RefMap.toRefMap;
 import static org.eclipse.jgit.lib.Constants.R_TAGS;
 import static org.eclipse.jgit.transport.GitProtocolConstants.CAPABILITY_REF_IN_WANT;
 import static org.eclipse.jgit.transport.GitProtocolConstants.COMMAND_FETCH;
@@ -817,7 +816,7 @@ private Map<String, Ref> getAdvertisedOrDefaultRefs() throws IOException {
 			// Fall back to all refs.
 			setAdvertisedRefs(
 					db.getRefDatabase().getRefs().stream()
-						.collect(toMap(Ref::getName, identity())));
+							.collect(toRefMap((a, b) -> b)));
 		}
 		return refs;
 	}
@@ -836,7 +835,7 @@ private Map<String, Ref> getFilteredRefs(Collection<String> refPrefixes)
 			String[] prefixes = refPrefixes.toArray(new String[0]);
 			Map<String, Ref> rs =
 					db.getRefDatabase().getRefsByPrefix(prefixes).stream()
-						.collect(toMap(Ref::getName, identity(), (a, b) -> b));
+							.collect(toRefMap((a, b) -> b));
 			if (refFilter != RefFilter.DEFAULT) {
 				return refFilter.filter(rs);
 			}
@@ -848,7 +847,7 @@ private Map<String, Ref> getFilteredRefs(Collection<String> refPrefixes)
 		return refs.values().stream()
 				.filter(ref -> refPrefixes.stream()
 						.anyMatch(ref.getName()::startsWith))
-				.collect(toMap(Ref::getName, identity()));
+				.collect(toRefMap((a, b) -> b));
 	}
 
 	/**
@@ -871,7 +870,7 @@ private static Map<String, Ref> mapRefs(
 				names.stream()
 					.map(refs::get)
 					.filter(Objects::nonNull)
-					.collect(toMap(Ref::getName, identity(), (a, b) -> b)));
+						.collect(toRefMap((a, b) -> b)));
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/RefList.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/RefList.java
index 639c35362..60dead51b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/RefList.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/RefList.java
@@ -48,7 +48,10 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.NoSuchElementException;
+import java.util.function.BinaryOperator;
+import java.util.stream.Collector;
 
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RefComparator;
 
@@ -332,6 +335,32 @@ public String toString() {
 		return r.toString();
 	}
 
+	/**
+	 * Create a {@link Collector} for {@link Ref}.
+	 *
+	 * @param mergeFunction
+	 *            if specified the result will be sorted and deduped.
+	 * @return {@link Collector} for {@link Ref}
+	 * @since 5.4
+	 */
+	public static <T extends Ref> Collector<T, ?, RefList<T>> toRefList(
+			@Nullable BinaryOperator<T> mergeFunction) {
+		return Collector.of(
+				() -> new Builder<>(),
+				Builder<T>::add, (b1, b2) -> {
+					Builder<T> b = new Builder<>();
+					b.addAll(b1);
+					b.addAll(b2);
+					return b;
+				}, (b) -> {
+					if (mergeFunction != null) {
+						b.sort();
+						b.dedupe(mergeFunction);
+					}
+					return b.toRefList();
+				});
+	}
+
 	/**
 	 * Builder to facilitate fast construction of an immutable RefList.
 	 *
@@ -404,6 +433,16 @@ public void add(T ref) {
 			list[size++] = ref;
 		}
 
+		/**
+		 * Add all items from another builder.
+		 *
+		 * @param other
+		 * @since 5.4
+		 */
+		public void addAll(Builder other) {
+			addAll(other.list, 0, other.size);
+		}
+
 		/**
 		 * Add all items from a source array.
 		 * <p>
@@ -444,6 +483,31 @@ public void sort() {
 			Arrays.sort(list, 0, size, RefComparator.INSTANCE);
 		}
 
+		/**
+		 * Dedupe the refs in place. Must be called after {@link #sort}.
+		 *
+		 * @param mergeFunction
+		 */
+		@SuppressWarnings("unchecked")
+		void dedupe(BinaryOperator<T> mergeFunction) {
+			if (size == 0) {
+				return;
+			}
+			int lastElement = 0;
+			for (int i = 1; i < size; i++) {
+				if (RefComparator.INSTANCE.compare(list[lastElement],
+						list[i]) == 0) {
+					list[lastElement] = mergeFunction
+							.apply((T) list[lastElement], (T) list[i]);
+				} else {
+					list[lastElement + 1] = list[i];
+					lastElement++;
+				}
+			}
+			size = lastElement + 1;
+			Arrays.fill(list, size, list.length, null);
+		}
+
 		/** @return an unmodifiable list using this collection's backing array. */
 		public RefList<T> toRefList() {
 			return new RefList<>(list, size);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/RefMap.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/RefMap.java
index a3f9730f1..d7a4c2535 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/RefMap.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/RefMap.java
@@ -49,6 +49,9 @@
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Set;
+import java.util.function.BinaryOperator;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
 
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.ObjectId;
@@ -285,6 +288,21 @@ public String toString() {
 		return r.toString();
 	}
 
+	/**
+	 * Create a {@link Collector} for {@link Ref}.
+	 *
+	 * @param mergeFunction
+	 * @return {@link Collector} for {@link Ref}
+	 * @since 5.4
+	 */
+	public static Collector<Ref, ?, RefMap> toRefMap(
+			BinaryOperator<Ref> mergeFunction) {
+		return Collectors.collectingAndThen(RefList.toRefList(mergeFunction),
+				(refs) -> new RefMap("", //$NON-NLS-1$
+							refs, RefList.emptyList(),
+						RefList.emptyList()));
+	}
+
 	private String toRefName(String name) {
 		if (0 < prefix.length())
 			name = prefix + name;