diff --git a/reviewboard/diffviewer/commitutils.py b/reviewboard/diffviewer/commitutils.py
new file mode 100644
index 0000000000000000000000000000000000000000..7338d2ffdfb0270440b0cee300a27d994f4b8bd4
--- /dev/null
+++ b/reviewboard/diffviewer/commitutils.py
@@ -0,0 +1,55 @@
+from __future__ import unicode_literals
+
+
+class DiffCommitFileExistenceChecker(object):
+    """A file existence checker for review requests with commit history."""
+
+    def __init__(self, repository, diffset, diff_commit):
+        """Initialize the file existence checker."""
+        self._repository = repository
+        self._diffset = diffset
+        self._diff_commit = diff_commit
+
+    def __call__(self, path, revision, base_commit_id=None, request=None):
+        """Check for the existence of the given file in the repository."""
+        from reviewboard.diffviewer.models import FileDiff
+
+        try:
+            filediff = self._diffset.files.get(dest_file=path,
+                                               dest_detail=revision)
+            parent_commit = filediff.diff_commit
+        except FileDiff.DoesNotExist:
+            # If we cannot find the file in the DiffSet's FileDiffs, we fall
+            # back to checking in the repository if it exists.
+            return self._repository.get_file_exists(
+                path,
+                revision,
+                base_commit_id=base_commit_id,
+                request=request)
+
+        # We must first make sure that the file exists.
+        if filediff.deleted:
+            return False
+
+        # Now that we've found the file, we should make sure that the commit it
+        # belongs to is an ancestor of the commit we are dealing with.
+
+        # We pass along the current DiffCommit because if we are doing commit
+        # validation, it will not be in the generated DAG because it was not
+        # saved to the database. However, if it is already in the DAG, it will
+        # be ignored.
+        dag = self._diffset.build_dag(self._diff_commit)
+        commit_id = self._diff_commit.commit_id
+
+        while commit_id in dag:
+            # We only support linear histories so this is a bit of a formality.
+            # once we support non-linear history, we will have to use a graph
+            # search algorithm like DFS/BFS.
+            assert len(dag[commit_id]) == 1
+
+            commit_id = dag[commit_id][0]
+
+            if commit_id == parent_commit.commit_id:
+                return True
+
+        return False
diff --git a/reviewboard/diffviewer/diffutils.py b/reviewboard/diffviewer/diffutils.py
index 19741f9ea1e810aee0a2964756f23661a290922d..89430a1f96bcaf2800f26b541bf7a0e0501427b6 100644
--- a/reviewboard/diffviewer/diffutils.py
+++ b/reviewboard/diffviewer/diffutils.py
@@ -806,56 +806,3 @@ def get_sorted_filediffs(filediffs, key=None):
             return filename[:i], filename[i + 1:]
 
     return sorted(filediffs, cmp=cmp_filediffs, key=make_key)
-
-
-class DiffCommitFileExistenceChecker(object):
-    """A file existence checker for review requests with commit history."""
-
-    def __init__(self, repository, diffset, diff_commit):
-        self._repository = repository
-        self._diffset = diffset
-        self._diff_commit = diff_commit
-
-    def __call__(self, path, revision, base_commit_id=None, request=None):
-        """Check for the existence of the given file in the repository."""
-        from reviewboard.diffviewer.models import FileDiff
-
-        try:
-            filediff = self._diffset.files.get(dest_file=path,
-                                               dest_detail=revision)
-            parent_commit = filediff.diff_commit
-        except FileDiff.DoesNotExist:
-            # If we cannot find the file in the DiffSet's FileDiffs, we fall
-            # back to checking in the repository if it exists.
-            return self._repository.get_file_exists(
-                path,
-                revision,
-                base_commit_id=base_commit_id,
-                request=request)
-
-        # We must first make sure that the file exists.
-        if filediff.deleted:
-            return False
-
-        # Now that we've found the file, we should make sure that the commit it
-        # belongs to is an ancestor of the commit we are dealing with.
-
-        # We pass along the current DiffCommit because if we are doing commit
-        # validation, it will not be in the generated DAG because it was not
-        # saved to the database. However, if it is already in the DAG, it will
-        # be ignored.
-        dag = self._diffset.build_dag(self._diff_commit)
-        commit_id = self._diff_commit.commit_id
-
-        while commit_id in dag:
-            # We only support linear histories so this is a bit of a formality.
-            # once we support non-linear history, we will have to use a graph
-            # search algorithm like DFS/BFS.
-            assert len(dag[commit_id]) == 1
-
-            commit_id = dag[commit_id][0]
-
-            if commit_id == parent_commit.commit_id:
-                return True
-
-        return False
diff --git a/reviewboard/diffviewer/managers.py b/reviewboard/diffviewer/managers.py
index c6d8fdb85d39bb95520b41e3b9c169f6ccbfa5ce..e1dce0e9695dc5e01507d4e240100ed3c22c5200 100644
--- a/reviewboard/diffviewer/managers.py
+++ b/reviewboard/diffviewer/managers.py
@@ -14,8 +14,8 @@ from django.utils.six.moves import range
 from django.utils.translation import ugettext as _
 from djblets.siteconfig.models import SiteConfiguration
 
+from reviewboard.diffviewer.commitutils import DiffCommitFileExistenceChecker
 from reviewboard.diffviewer.differ import DiffCompatVersion
-from reviewboard.diffviewer.diffutils import DiffCommitFileExistenceChecker
 from reviewboard.diffviewer.errors import DiffTooBigError, EmptyDiffError
 from reviewboard.scmtools.core import PRE_CREATION, UNKNOWN, FileNotFoundError