diff --git a/CHANGES.md b/CHANGES.md
index 4515786d3f..abc9799ba6 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -14,6 +14,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * `LineEnding.GIT_ATTRIBUTES` now creates a policy whose serialized state can be relocated from one machine to another.  No user-visible change, but paves the way for remote build cache support in Gradle. ([#621](https://github.com/diffplug/spotless/pull/621))
 ### Added
 * `prettier` will now autodetect the parser (and formatter) to use based on the filename, unless you override this using `config` or `configFile` with the option `parser` or `filepath`. ([#620](https://github.com/diffplug/spotless/pull/620))
+* `GitRatchet` now lives in `lib-extra`, and is shared across `plugin-gradle` and `plugin-maven` ([#626](https://github.com/diffplug/spotless/pull/626)).
 ### Changed
 * **BREAKING** `FileSignature` can no longer sign folders, only files.  Signatures are now based only on filename (not path), size, and a content hash.  It throws an error if a signature is attempted on a folder or on multiple files with different paths but the same filename - it never breaks silently.  This change does not break any of Spotless' internal logic, so it is unlikely to affect any of Spotless' consumers either. ([#571](https://github.com/diffplug/spotless/pull/571))
   * This change allows the maven plugin to cache classloaders across subprojects when loading config resources from the classpath (fixes [#559](https://github.com/diffplug/spotless/issues/559)).
diff --git a/gradle.properties b/gradle.properties
index 1333215701..9770f4eeb6 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -22,7 +22,7 @@ VER_SLF4J=[1.6,2.0[
 
 # Used in multiple places
 VER_DURIAN=1.2.0
-VER_JGIT=5.7.0.202003110725-r
+VER_JGIT=5.8.0.202006091008-r
 VER_JUNIT=4.13
 VER_ASSERTJ=3.15.0
 VER_MOCKITO=3.3.3
diff --git a/lib-extra/src/main/java/com/diffplug/spotless/extra/GitRatchet.java b/lib-extra/src/main/java/com/diffplug/spotless/extra/GitRatchet.java
index fe06f43183..b71731b4e5 100644
--- a/lib-extra/src/main/java/com/diffplug/spotless/extra/GitRatchet.java
+++ b/lib-extra/src/main/java/com/diffplug/spotless/extra/GitRatchet.java
@@ -20,6 +20,7 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 
 import javax.annotation.Nullable;
 
@@ -31,6 +32,7 @@
 import org.eclipse.jgit.lib.RepositoryCache;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.revwalk.filter.RevFilter;
 import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
 import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.FileTreeIterator;
@@ -195,13 +197,21 @@ public synchronized ObjectId rootTreeShaOf(Project project, String reference) {
 			Repository repo = repositoryFor(project);
 			ObjectId treeSha = rootTreeShaCache.get(repo, reference);
 			if (treeSha == null) {
-				ObjectId commitSha = repo.resolve(reference);
-				if (commitSha == null) {
-					throw new IllegalArgumentException("No such reference '" + reference + "'");
-				}
 				try (RevWalk revWalk = new RevWalk(repo)) {
-					RevCommit revCommit = revWalk.parseCommit(commitSha);
-					treeSha = revCommit.getTree();
+					ObjectId commitSha = repo.resolve(reference);
+					if (commitSha == null) {
+						throw new IllegalArgumentException("No such reference '" + reference + "'");
+					}
+
+					RevCommit ratchetFrom = revWalk.parseCommit(commitSha);
+					RevCommit head = revWalk.parseCommit(repo.resolve(Constants.HEAD));
+
+					revWalk.setRevFilter(RevFilter.MERGE_BASE);
+					revWalk.markStart(ratchetFrom);
+					revWalk.markStart(head);
+
+					RevCommit mergeBase = revWalk.next();
+					treeSha = Optional.ofNullable(mergeBase).orElse(ratchetFrom).getTree();
 				}
 				rootTreeShaCache.put(repo, reference, treeSha);
 			}
diff --git a/lib-extra/src/test/java/com/diffplug/spotless/extra/GitRachetMergeBaseTest.java b/lib-extra/src/test/java/com/diffplug/spotless/extra/GitRachetMergeBaseTest.java
new file mode 100644
index 0000000000..e13b40a2b2
--- /dev/null
+++ b/lib-extra/src/test/java/com/diffplug/spotless/extra/GitRachetMergeBaseTest.java
@@ -0,0 +1,132 @@
+/*
+ * Copyright 2020 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless.extra;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.RefDatabase;
+import org.junit.Test;
+
+import com.diffplug.spotless.ResourceHarness;
+
+public class GitRachetMergeBaseTest extends ResourceHarness {
+	@Test
+	public void test() throws IllegalStateException, GitAPIException, IOException {
+		try (Git git = initRepo()) {
+			setFile("mine.txt").toContent("init");
+			setFile("untouched.txt").toContent("init");
+			addAndCommit(git, "init");
+
+			git.checkout().setCreateBranch(true).setName("rem-branch").call();
+			// so at the point where we start work, we are clean relative to the remote
+			ratchetFrom("main", "rem-branch").allClean();
+
+			// but when the remote changes
+			setFile("untouched.txt").toContent("changed");
+			addAndCommit(git, "remote");
+
+			// it shouldn't affect files that we haven't changed
+			git.checkout().setName("main").call();
+			ratchetFrom("main", "rem-branch").allClean();
+
+			// and when we work, it should continue to only affect our own work
+			setFile("mine.txt").toContent("changed");
+			ratchetFrom("main", "rem-branch").onlyDirty("mine.txt");
+		}
+	}
+
+	static class GitRatchetSimple extends GitRatchet<File> {
+		@Override
+		protected File getDir(File project) {
+			return project;
+		}
+
+		@Override
+		protected File getParent(File project) {
+			return project.getParentFile();
+		}
+	}
+
+	Asserter ratchetFrom(String... ratchetFroms) {
+		return new Asserter(ratchetFroms);
+	}
+
+	class Asserter {
+		final GitRatchetSimple ratchet = new GitRatchetSimple();
+		final String[] ratchetFroms;
+		final ObjectId[] shas;
+
+		Asserter(String... ratchetFrom) {
+			this.ratchetFroms = ratchetFrom;
+			this.shas = Arrays.stream(ratchetFrom)
+					.map(from -> ratchet.rootTreeShaOf(rootFolder(), from))
+					.toArray(ObjectId[]::new);
+		}
+
+		private void assertClean(int i, String filename, boolean expected) throws IOException {
+			boolean actual = ratchet.isClean(rootFolder(), shas[i], newFile(filename));
+			if (actual != expected) {
+				throw new AssertionError("Expected " + filename + " to be " + (expected ? "clean" : "dirty") + " relative to " + ratchetFroms[i]);
+			}
+		}
+
+		public void allClean() throws IOException {
+			onlyDirty();
+		}
+
+		public void allDirty() throws IOException {
+			String[] filenames = Arrays.stream(rootFolder().listFiles())
+					.filter(File::isFile)
+					.map(File::getName)
+					.toArray(String[]::new);
+			onlyDirty(filenames);
+		}
+
+		public void onlyDirty(String... filenames) throws IOException {
+			List<String> dirtyFiles = Arrays.asList(filenames);
+			for (File file : rootFolder().listFiles()) {
+				if (!file.isFile()) {
+					continue;
+				}
+				boolean expectedClean = !dirtyFiles.contains(file.getName());
+				for (int i = 0; i < shas.length; ++i) {
+					assertClean(i, file.getName(), expectedClean);
+				}
+			}
+		}
+	}
+
+	private Git initRepo() throws IllegalStateException, GitAPIException, IOException {
+		Git git = Git.init().setDirectory(rootFolder()).call();
+		RefDatabase refDB = git.getRepository().getRefDatabase();
+		refDB.newUpdate(Constants.R_HEADS + "main", false).setNewObjectId(ObjectId.zeroId());
+		refDB.newUpdate(Constants.HEAD, false).link(Constants.R_HEADS + "main");
+		refDB.newUpdate(Constants.R_HEADS + Constants.MASTER, false).delete();
+		return git;
+	}
+
+	private void addAndCommit(Git git, String message) throws GitAPIException {
+		git.add().addFilepattern(".").call();
+		git.commit().setMessage(message).call();
+	}
+}
diff --git a/plugin-gradle/CHANGES.md b/plugin-gradle/CHANGES.md
index 8e2124f016..fae34fcaee 100644
--- a/plugin-gradle/CHANGES.md
+++ b/plugin-gradle/CHANGES.md
@@ -10,6 +10,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * `prettier` will now autodetect the parser (and formatter) to use based on the filename, unless you override this using `config()` or `configFile()` with the option `parser` or `filepath`. ([#620](https://github.com/diffplug/spotless/pull/620))
 ### Fixed
 * LineEndings.GIT_ATTRIBUTES is now a bit more efficient, and paves the way for remote build cache support in Gradle. ([#621](https://github.com/diffplug/spotless/pull/621))
+* `ratchetFrom` now ratchets from the merge base of `HEAD` and the specified branch.  This fixes the surprising behavior when a remote branch advanced ([#631](https://github.com/diffplug/spotless/pull/631) fixes [#627](https://github.com/diffplug/spotless/issues/627)).
 
 ## [4.4.0] - 2020-06-19
 ### Added