diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/FileInfoJson.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/FileInfoJson.java
index e0591f4683..8e55df549a 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/FileInfoJson.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/FileInfoJson.java
@@ -14,8 +14,6 @@
 
 package com.google.gerrit.server.change;
 
-import static com.google.gerrit.server.util.GitUtil.getParent;
-
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
 import com.google.gerrit.extensions.common.FileInfo;
@@ -23,7 +21,6 @@ import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Patch;
 import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.RevId;
-import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.patch.PatchList;
 import com.google.gerrit.server.patch.PatchListCache;
 import com.google.gerrit.server.patch.PatchListEntry;
@@ -32,24 +29,18 @@ import com.google.gerrit.server.patch.PatchListNotAvailableException;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 
-import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Repository;
 
-import java.io.IOException;
 import java.util.Map;
 import java.util.TreeMap;
 
 @Singleton
 public class FileInfoJson {
   private final PatchListCache patchListCache;
-  private final GitRepositoryManager repoManager;
 
   @Inject
   FileInfoJson(
-      PatchListCache patchListCache,
-      GitRepositoryManager repoManager) {
-    this.repoManager = repoManager;
+      PatchListCache patchListCache) {
     this.patchListCache = patchListCache;
   }
 
@@ -64,24 +55,19 @@ public class FileInfoJson {
         ? null
         : ObjectId.fromString(base.getRevision().get());
     ObjectId b = ObjectId.fromString(revision.get());
-    return toFileInfoMap(change, a, b);
+    return toFileInfoMap(change, new PatchListKey(a, b, Whitespace.IGNORE_NONE));
   }
 
   Map<String, FileInfo> toFileInfoMap(Change change, RevId revision, int parent)
-      throws RepositoryNotFoundException, IOException,
-          PatchListNotAvailableException {
+      throws PatchListNotAvailableException {
     ObjectId b = ObjectId.fromString(revision.get());
-    ObjectId a;
-    try (Repository git = repoManager.openRepository(change.getProject())) {
-      a = getParent(git, b, parent);
-    }
-    return toFileInfoMap(change, a, b);
+    return toFileInfoMap(change,
+        PatchListKey.againstParentNum(parent + 1, b, Whitespace.IGNORE_NONE));
   }
 
   private Map<String, FileInfo> toFileInfoMap(Change change,
-      ObjectId a, ObjectId b) throws PatchListNotAvailableException {
-    PatchList list = patchListCache.get(
-        new PatchListKey(a, b, Whitespace.IGNORE_NONE), change.getProject());
+      PatchListKey key) throws PatchListNotAvailableException {
+    PatchList list = patchListCache.get(key, change.getProject());
 
     Map<String, FileInfo> files = new TreeMap<>();
     for (PatchListEntry e : list.getPatches()) {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchScriptFactory.java b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchScriptFactory.java
index a7d2523136..754d9950a3 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchScriptFactory.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchScriptFactory.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.server.patch;
 
 import static com.google.common.base.Preconditions.checkArgument;
-import static com.google.gerrit.server.util.GitUtil.getParent;
 
 import com.google.common.base.Optional;
 import com.google.gerrit.common.Nullable;
@@ -214,8 +213,6 @@ public class PatchScriptFactory implements Callable<PatchScript> {
       bId = toObjectId(psEntityB);
       if (parentNum < 0) {
         aId = psEntityA != null ? toObjectId(psEntityA) : null;
-      } else {
-        aId = getParent(git, bId, parentNum);
       }
 
       try {
@@ -247,7 +244,10 @@ public class PatchScriptFactory implements Callable<PatchScript> {
   }
 
   private PatchListKey keyFor(final Whitespace whitespace) {
-    return new PatchListKey(aId, bId, whitespace);
+    if (parentNum < 0) {
+      return new PatchListKey(aId, bId, whitespace);
+    }
+    return PatchListKey.againstParentNum(parentNum + 1, bId, whitespace);
   }
 
   private PatchList listFor(final PatchListKey key)
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/util/GitUtil.java b/gerrit-server/src/main/java/com/google/gerrit/server/util/GitUtil.java
deleted file mode 100644
index 2d1e1fa4e9..0000000000
--- a/gerrit-server/src/main/java/com/google/gerrit/server/util/GitUtil.java
+++ /dev/null
@@ -1,51 +0,0 @@
-// Copyright (C) 2016 The Android Open Source Project
-//
-// 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.google.gerrit.server.util;
-
-import org.eclipse.jgit.errors.IncorrectObjectTypeException;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-
-import java.io.IOException;
-
-public class GitUtil {
-
-  /**
-   * @param git
-   * @param commitId
-   * @param parentNum
-   * @return the {@code paretNo} parent of given commit or {@code null}
-   *             when {@code parentNo} exceed number of {@code commitId} parents.
-   * @throws IncorrectObjectTypeException
-   *             the supplied id is not a commit or an annotated tag.
-   * @throws IOException
-   *             a pack file or loose object could not be read.
-   */
-  public static RevCommit getParent(Repository git,
-      ObjectId commitId, int parentNum) throws IOException {
-    try (RevWalk walk = new RevWalk(git)) {
-      RevCommit commit = walk.parseCommit(commitId);
-      if (commit.getParentCount() > parentNum) {
-        return commit.getParent(parentNum);
-      }
-    }
-    return null;
-  }
-
-  private GitUtil() {
-  }
-}