diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCache.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCache.java
index 530227d..d0c6fe5 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCache.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCache.java
@@ -21,5 +21,13 @@
 import java.util.List;
 
 public interface BlameCache {
+  /** @return the blame of a path at a given commit. */
   public List<Region> get(Repository repo, ObjectId commitId, String path) throws IOException;
+
+  /**
+   * @return the last commit that modified a path, starting at the given
+   *     commit.
+   */
+  public ObjectId findLastCommit(Repository repo, ObjectId commitId, String path)
+      throws IOException;
 }
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
index 459bccd..50b2d8f 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
@@ -31,6 +31,10 @@
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.treewalk.filter.AndTreeFilter;
+import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
+import org.eclipse.jgit.treewalk.filter.TreeFilter;
 import org.eclipse.jgit.util.QuotedString;
 
 import java.io.IOException;
@@ -124,6 +128,26 @@
     }
   }
 
+  @Override
+  public ObjectId findLastCommit(Repository repo, ObjectId commitId, String path)
+      throws IOException {
+    // Default implementation does no caching.
+    RevWalk rw = new RevWalk(repo);
+    try {
+      rw.markStart(rw.parseCommit(commitId));
+      rw.setRewriteParents(false);
+      // Don't use rename detection, even though BlameGenerator does. It is not
+      // possible for a commit to modify a path when not doing rename detection
+      // but to not modify the same path when taking renames into account.
+      rw.setTreeFilter(AndTreeFilter.create(
+          PathFilterGroup.createFromStrings(path),
+          TreeFilter.ANY_DIFF));
+      return rw.next();
+    } finally {
+      rw.release();
+    }
+  }
+
   public static List<Region> loadBlame(Key key) throws IOException {
     try {
       BlameGenerator gen = new BlameGenerator(key.repo, key.path);
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
index 9c3fab7..04e86a8 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
@@ -41,11 +41,9 @@
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.TreeWalk;
-import org.eclipse.jgit.treewalk.filter.AndTreeFilter;
-import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
-import org.eclipse.jgit.treewalk.filter.TreeFilter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -84,7 +82,7 @@
         return;
       }
 
-      RevCommit lastCommit = findLastCommit(rw, currCommit, view.getPathPart());
+      ObjectId lastCommit = cache.findLastCommit(repo, currCommit, view.getPathPart());
       ObjectId lastCommitBlobId = resolveBlob(view, rw, lastCommit);
 
       if (!Objects.equal(currCommitBlobId, lastCommitBlobId)) {
@@ -125,30 +123,14 @@
     }
   }
 
-  private static RevCommit findLastCommit(RevWalk rw, RevCommit curr, String path)
-      throws IOException {
-    rw.markStart(curr);
-    rw.setRewriteParents(false);
-    // Don't use rename detection, even though BlameGenerator does. It is not
-    // possible for a commit to modify a path when not doing rename detection
-    // but to not modify the same path when taking renames into account.
-    rw.setTreeFilter(AndTreeFilter.create(
-        PathFilterGroup.createFromStrings(path),
-        TreeFilter.ANY_DIFF));
-    try {
-      return rw.next();
-    } finally {
-      rw.reset();
-    }
-  }
-
-  private static ObjectId resolveBlob(GitilesView view, RevWalk rw, RevCommit commit)
+  private static ObjectId resolveBlob(GitilesView view, RevWalk rw, ObjectId commitId)
       throws IOException {
     try {
-      if (commit == null || Strings.isNullOrEmpty(view.getPathPart())) {
+      if (commitId == null || Strings.isNullOrEmpty(view.getPathPart())) {
         return null;
       }
-      TreeWalk tw = TreeWalk.forPath(rw.getObjectReader(), view.getPathPart(), commit.getTree());
+      RevTree tree = rw.parseTree(commitId);
+      TreeWalk tw = TreeWalk.forPath(rw.getObjectReader(), view.getPathPart(), tree);
       if (tw == null || (tw.getRawMode(0) & FileMode.TYPE_FILE) == 0) {
         return null;
       }