diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
index f9bdb2f..091b02c 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
@@ -91,6 +91,8 @@
         persist(DIFF, FileDiffCacheKey.class, FileDiffOutput.class)
             .maximumWeight(10 << 20)
             .weigher(FileDiffWeigher.class)
+            .keySerializer(FileDiffCacheKey.Serializer.INSTANCE)
+            .valueSerializer(FileDiffOutput.Serializer.INSTANCE)
             .loader(FileDiffLoader.class);
       }
     };
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
index 5e45da29..a478fcf 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
@@ -21,6 +21,10 @@
 import com.google.gerrit.entities.Project.NameKey;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
+import com.google.gerrit.proto.Protos;
+import com.google.gerrit.server.cache.proto.Cache.FileDiffKeyProto;
+import com.google.gerrit.server.cache.serialize.CacheSerializer;
+import com.google.gerrit.server.cache.serialize.ObjectIdConverter;
 import com.google.gerrit.server.patch.gitfilediff.GitFileDiffCacheImpl.DiffAlgorithm;
 import org.eclipse.jgit.lib.ObjectId;
 
@@ -89,4 +93,38 @@
 
     public abstract FileDiffCacheKey build();
   }
+
+  public enum Serializer implements CacheSerializer<FileDiffCacheKey> {
+    INSTANCE;
+
+    @Override
+    public byte[] serialize(FileDiffCacheKey key) {
+      ObjectIdConverter idConverter = ObjectIdConverter.create();
+      return Protos.toByteArray(
+          FileDiffKeyProto.newBuilder()
+              .setProject(key.project().get())
+              .setOldCommit(idConverter.toByteString(key.oldCommit()))
+              .setNewCommit(idConverter.toByteString(key.newCommit()))
+              .setFilePath(key.newFilePath())
+              .setRenameScore(key.renameScore())
+              .setDiffAlgorithm(key.diffAlgorithm().name())
+              .setWhitespace(key.whitespace().name())
+              .build());
+    }
+
+    @Override
+    public FileDiffCacheKey deserialize(byte[] in) {
+      FileDiffKeyProto proto = Protos.parseUnchecked(FileDiffKeyProto.parser(), in);
+      ObjectIdConverter idConverter = ObjectIdConverter.create();
+      return FileDiffCacheKey.builder()
+          .project(Project.nameKey(proto.getProject()))
+          .oldCommit(idConverter.fromByteString(proto.getOldCommit()))
+          .newCommit(idConverter.fromByteString(proto.getNewCommit()))
+          .newFilePath(proto.getFilePath())
+          .renameScore(proto.getRenameScore())
+          .diffAlgorithm(DiffAlgorithm.valueOf(proto.getDiffAlgorithm()))
+          .whitespace(Whitespace.valueOf(proto.getWhitespace()))
+          .build();
+    }
+  }
 }
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java b/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
index c161cfa..e89f148 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
@@ -21,8 +21,13 @@
 import com.google.gerrit.entities.Patch;
 import com.google.gerrit.entities.Patch.ChangeType;
 import com.google.gerrit.entities.Patch.PatchType;
+import com.google.gerrit.proto.Protos;
+import com.google.gerrit.server.cache.proto.Cache.FileDiffOutputProto;
+import com.google.gerrit.server.cache.serialize.CacheSerializer;
+import com.google.protobuf.Descriptors.FieldDescriptor;
 import java.io.Serializable;
 import java.util.Optional;
+import java.util.stream.Collectors;
 
 /** File diff for a single file path. Produced as output of the {@link FileDiffCache}. */
 @AutoValue
@@ -105,7 +110,7 @@
     return headerLines().isEmpty() && edits().isEmpty();
   }
 
-  static Builder builder() {
+  public static Builder builder() {
     return new AutoValue_FileDiffOutput.Builder();
   }
 
@@ -153,4 +158,98 @@
 
     public abstract FileDiffOutput build();
   }
+
+  public enum Serializer implements CacheSerializer<FileDiffOutput> {
+    INSTANCE;
+
+    private static final FieldDescriptor OLD_PATH_DESCRIPTOR =
+        FileDiffOutputProto.getDescriptor().findFieldByNumber(1);
+
+    private static final FieldDescriptor NEW_PATH_DESCRIPTOR =
+        FileDiffOutputProto.getDescriptor().findFieldByNumber(2);
+
+    private static final FieldDescriptor CHANGE_TYPE_DESCRIPTOR =
+        FileDiffOutputProto.getDescriptor().findFieldByNumber(3);
+
+    private static final FieldDescriptor PATCH_TYPE_DESCRIPTOR =
+        FileDiffOutputProto.getDescriptor().findFieldByNumber(4);
+
+    @Override
+    public byte[] serialize(FileDiffOutput fileDiff) {
+      FileDiffOutputProto.Builder builder =
+          FileDiffOutputProto.newBuilder()
+              .setSize(fileDiff.size())
+              .setSizeDelta(fileDiff.sizeDelta())
+              .addAllHeaderLines(fileDiff.headerLines())
+              .addAllEdits(
+                  fileDiff.edits().stream()
+                      .map(
+                          e ->
+                              FileDiffOutputProto.TaggedEdit.newBuilder()
+                                  .setEdit(
+                                      FileDiffOutputProto.Edit.newBuilder()
+                                          .setBeginA(e.edit().beginA())
+                                          .setEndA(e.edit().endA())
+                                          .setBeginB(e.edit().beginB())
+                                          .setEndB(e.edit().endB())
+                                          .build())
+                                  .setDueToRebase(e.dueToRebase())
+                                  .build())
+                      .collect(Collectors.toList()));
+
+      if (fileDiff.oldPath().isPresent()) {
+        builder.setOldPath(fileDiff.oldPath().get());
+      }
+
+      if (fileDiff.newPath().isPresent()) {
+        builder.setNewPath(fileDiff.newPath().get());
+      }
+
+      if (fileDiff.changeType().isPresent()) {
+        builder.setChangeType(fileDiff.changeType().get().name());
+      }
+
+      if (fileDiff.patchType().isPresent()) {
+        builder.setPatchType(fileDiff.patchType().get().name());
+      }
+
+      return Protos.toByteArray(builder.build());
+    }
+
+    @Override
+    public FileDiffOutput deserialize(byte[] in) {
+      FileDiffOutputProto proto = Protos.parseUnchecked(FileDiffOutputProto.parser(), in);
+      FileDiffOutput.Builder builder = FileDiffOutput.builder();
+      builder
+          .size(proto.getSize())
+          .sizeDelta(proto.getSizeDelta())
+          .headerLines(proto.getHeaderLinesList().stream().collect(ImmutableList.toImmutableList()))
+          .edits(
+              proto.getEditsList().stream()
+                  .map(
+                      e ->
+                          TaggedEdit.create(
+                              Edit.create(
+                                  e.getEdit().getBeginA(),
+                                  e.getEdit().getEndA(),
+                                  e.getEdit().getBeginB(),
+                                  e.getEdit().getEndB()),
+                              e.getDueToRebase()))
+                  .collect(ImmutableList.toImmutableList()));
+
+      if (proto.hasField(OLD_PATH_DESCRIPTOR)) {
+        builder.oldPath(Optional.of(proto.getOldPath()));
+      }
+      if (proto.hasField(NEW_PATH_DESCRIPTOR)) {
+        builder.newPath(Optional.of(proto.getNewPath()));
+      }
+      if (proto.hasField(CHANGE_TYPE_DESCRIPTOR)) {
+        builder.changeType(Optional.of(Patch.ChangeType.valueOf(proto.getChangeType())));
+      }
+      if (proto.hasField(PATCH_TYPE_DESCRIPTOR)) {
+        builder.patchType(Optional.of(Patch.PatchType.valueOf(proto.getPatchType())));
+      }
+      return builder.build();
+    }
+  }
 }
diff --git a/java/com/google/gerrit/server/patch/gitdiff/ModifiedFile.java b/java/com/google/gerrit/server/patch/gitdiff/ModifiedFile.java
index 800bd41..9512094 100644
--- a/java/com/google/gerrit/server/patch/gitdiff/ModifiedFile.java
+++ b/java/com/google/gerrit/server/patch/gitdiff/ModifiedFile.java
@@ -79,10 +79,10 @@
     INSTANCE;
 
     private static final FieldDescriptor oldPathDescriptor =
-        ModifiedFileProto.getDescriptor().findFieldByName("old_path");
+        ModifiedFileProto.getDescriptor().findFieldByNumber(2);
 
     private static final FieldDescriptor newPathDescriptor =
-        ModifiedFileProto.getDescriptor().findFieldByName("new_path");
+        ModifiedFileProto.getDescriptor().findFieldByNumber(3);
 
     @Override
     public byte[] serialize(ModifiedFile modifiedFile) {
diff --git a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiff.java b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiff.java
index 7d1c24e..6d63243 100644
--- a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiff.java
+++ b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiff.java
@@ -202,22 +202,22 @@
     INSTANCE;
 
     private static final FieldDescriptor OLD_PATH_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("old_path");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(3);
 
     private static final FieldDescriptor NEW_PATH_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("new_path");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(4);
 
     private static final FieldDescriptor OLD_MODE_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("old_mode");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(7);
 
     private static final FieldDescriptor NEW_MODE_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("new_mode");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(8);
 
     private static final FieldDescriptor CHANGE_TYPE_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("change_type");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(9);
 
     private static final FieldDescriptor PATCH_TYPE_DESCRIPTOR =
-        GitFileDiffProto.getDescriptor().findFieldByName("patch_type");
+        GitFileDiffProto.getDescriptor().findFieldByNumber(10);
 
     @Override
     public byte[] serialize(GitFileDiff gitFileDiff) {
diff --git a/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffCacheKeySerializerTest.java b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffCacheKeySerializerTest.java
new file mode 100644
index 0000000..ecab07d
--- /dev/null
+++ b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffCacheKeySerializerTest.java
@@ -0,0 +1,50 @@
+// Copyright (C) 2020 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.cache.serialize.entities;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.gerrit.entities.Project;
+import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
+import com.google.gerrit.server.patch.filediff.FileDiffCacheKey;
+import com.google.gerrit.server.patch.gitfilediff.GitFileDiffCacheImpl.DiffAlgorithm;
+import org.eclipse.jgit.lib.ObjectId;
+import org.junit.Test;
+
+/** Tests the protobuf serializer for the {@link FileDiffCacheKey}. */
+public class FileDiffCacheKeySerializerTest {
+  private static final ObjectId COMMIT_ID_1 =
+      ObjectId.fromString("123e9fa8a286255ac7d5ba11b598892735758391");
+  private static final ObjectId COMMIT_ID_2 =
+      ObjectId.fromString("d07a03a9818c120301cb5b4a969b035479400b5f");
+
+  @Test
+  public void roundTrip() {
+    FileDiffCacheKey key =
+        FileDiffCacheKey.builder()
+            .project(Project.nameKey("project/x"))
+            .oldCommit(COMMIT_ID_1)
+            .newCommit(COMMIT_ID_2)
+            .newFilePath("some_file.txt")
+            .renameScore(65)
+            .diffAlgorithm(DiffAlgorithm.HISTOGRAM)
+            .whitespace(Whitespace.IGNORE_ALL)
+            .build();
+
+    byte[] serialized = FileDiffCacheKey.Serializer.INSTANCE.serialize(key);
+
+    assertThat(FileDiffCacheKey.Serializer.INSTANCE.deserialize(serialized)).isEqualTo(key);
+  }
+}
diff --git a/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java
new file mode 100644
index 0000000..4307954
--- /dev/null
+++ b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java
@@ -0,0 +1,51 @@
+// Copyright (C) 2020 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.cache.serialize.entities;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.entities.Patch.ChangeType;
+import com.google.gerrit.entities.Patch.PatchType;
+import com.google.gerrit.server.patch.filediff.Edit;
+import com.google.gerrit.server.patch.filediff.FileDiffOutput;
+import com.google.gerrit.server.patch.filediff.TaggedEdit;
+import java.util.Optional;
+import org.junit.Test;
+
+public class FileDiffOutputSerializerTest {
+  @Test
+  public void roundTrip() {
+    ImmutableList<TaggedEdit> edits =
+        ImmutableList.of(
+            TaggedEdit.create(Edit.create(1, 5, 3, 4), true),
+            TaggedEdit.create(Edit.create(21, 30, 150, 158), false));
+
+    FileDiffOutput fileDiff =
+        FileDiffOutput.builder()
+            .oldPath(Optional.of("old_file_path.txt"))
+            .newPath(Optional.empty())
+            .changeType(Optional.of(ChangeType.DELETED))
+            .patchType(Optional.of(PatchType.UNIFIED))
+            .size(23)
+            .sizeDelta(10)
+            .headerLines(ImmutableList.of("header line 1", "header line 2"))
+            .edits(edits)
+            .build();
+
+    byte[] serialized = FileDiffOutput.Serializer.INSTANCE.serialize(fileDiff);
+    assertThat(FileDiffOutput.Serializer.INSTANCE.deserialize(serialized)).isEqualTo(fileDiff);
+  }
+}
diff --git a/proto/cache.proto b/proto/cache.proto
index 0676f1b..8d575b7 100644
--- a/proto/cache.proto
+++ b/proto/cache.proto
@@ -599,3 +599,43 @@
   string change_type = 9; // ENUM as string
   string patch_type = 10; // ENUM as string
 }
+
+// Serialized form of
+// com.google.gerrit.server.patch.fileDiff.FileDiffCacheKey
+// Next ID: 8
+message FileDiffKeyProto {
+  string project = 1;
+  bytes old_commit = 2;
+  bytes new_commit = 3;
+  string file_path = 4;
+  int32 rename_score = 5;
+  string diff_algorithm = 6;
+  string whitespace = 7;
+}
+
+// Serialized form of
+// com.google.gerrit.server.patch.filediff.FileDiffOutput
+// Next ID: 9
+message FileDiffOutputProto {
+  // Next ID: 5
+  message Edit {
+    int32 begin_a = 1;
+    int32 end_a = 2;
+    int32 begin_b = 3;
+    int32 end_b = 4;
+  }
+  // Serialized form  of com.google.gerrit.server.patch.filediff.TaggedEdit
+  // Next ID: 3
+  message TaggedEdit {
+    Edit edit = 1;
+    bool due_to_rebase = 2;
+  }
+  string old_path = 1;
+  string new_path = 2;
+  string change_type = 3;
+  string patch_type = 4;
+  repeated string header_lines = 5;
+  int64 size = 6;
+  int64 size_delta = 7;
+  repeated TaggedEdit edits = 8;
+}