diff --git a/generator/internal/codegen_utils.cc b/generator/internal/codegen_utils.cc
index d07c95619e1fe..be0b8ff6f26ce 100644
--- a/generator/internal/codegen_utils.cc
+++ b/generator/internal/codegen_utils.cc
@@ -26,6 +26,11 @@
 #include <cctype>
 #include <string>
 #include <unordered_set>
+#if _WIN32
+#include <direct.h>
+#else
+#include <sys/stat.h>
+#endif  // _WIN32
 
 namespace google {
 namespace cloud {
@@ -380,6 +385,14 @@ std::string FormatHeaderIncludeGuard(absl::string_view header_path) {
                           {{"/", "_"}, {".", "_"}}));
 }
 
+void MakeDirectory(std::string const& path) {
+#if _WIN32
+  _mkdir(path.c_str());
+#else
+  mkdir(path.c_str(), 0755);
+#endif  // _WIN32
+}
+
 }  // namespace generator_internal
 }  // namespace cloud
 }  // namespace google
diff --git a/generator/internal/codegen_utils.h b/generator/internal/codegen_utils.h
index 4eb8c26f065d3..1b24354b68be8 100644
--- a/generator/internal/codegen_utils.h
+++ b/generator/internal/codegen_utils.h
@@ -130,6 +130,9 @@ std::string FormatCommentKeyValueList(
 // Formats a header include guard per the provided header_path.
 std::string FormatHeaderIncludeGuard(absl::string_view header_path);
 
+/// Create a directory. The parent must exist.
+void MakeDirectory(std::string const& path);
+
 }  // namespace generator_internal
 }  // namespace cloud
 }  // namespace google
diff --git a/generator/internal/discovery_file.cc b/generator/internal/discovery_file.cc
index bd5a2a73d7d17..e76ca853afec0 100644
--- a/generator/internal/discovery_file.cc
+++ b/generator/internal/discovery_file.cc
@@ -19,25 +19,12 @@
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
 #include <fstream>
-#ifdef _WIN32
-#include <direct.h>
-#else
-#include <sys/stat.h>
-#endif  // _WIN32
 
 namespace google {
 namespace cloud {
 namespace generator_internal {
 namespace {
 
-void MakeDirectory(std::string const& path) {
-#if _WIN32
-  _mkdir(path.c_str());
-#else
-  mkdir(path.c_str(), 0777);
-#endif  // _WIN32
-}
-
 std::string GeneratedProtoPreamble() {
   auto constexpr kPreamble = R"""(
 // Generated by the C++ microgenerator.
diff --git a/generator/internal/discovery_proto_export_file.cc b/generator/internal/discovery_proto_export_file.cc
index 9a08bb246c582..cecd30328e852 100644
--- a/generator/internal/discovery_proto_export_file.cc
+++ b/generator/internal/discovery_proto_export_file.cc
@@ -19,27 +19,10 @@
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
 #include <fstream>
-#ifdef _WIN32
-#include <direct.h>
-#else
-#include <sys/stat.h>
-#endif  // _WIN32
 
 namespace google {
 namespace cloud {
 namespace generator_internal {
-namespace {
-
-// TODO(#12818): refactor this function to single translation unit.
-void MakeDirectory(std::string const& path) {
-#if _WIN32
-  _mkdir(path.c_str());
-#else
-  mkdir(path.c_str(), 0777);
-#endif  // _WIN32
-}
-
-}  // namespace
 
 DiscoveryProtoExportFile::DiscoveryProtoExportFile(
     std::string output_file_path, std::string relative_file_path,
diff --git a/generator/internal/scaffold_generator.cc b/generator/internal/scaffold_generator.cc
index e1845b73a6840..5b1976c023528 100644
--- a/generator/internal/scaffold_generator.cc
+++ b/generator/internal/scaffold_generator.cc
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 #include "generator/internal/scaffold_generator.h"
+#include "generator/internal/codegen_utils.h"
 #include "google/cloud/internal/absl_str_join_quiet.h"
 #include "google/cloud/internal/absl_str_replace_quiet.h"
 #include "google/cloud/internal/filesystem.h"
@@ -25,11 +26,6 @@
 #include <fstream>
 #include <iterator>
 #include <regex>
-#ifdef _WIN32
-#include <direct.h>
-#else
-#include <sys/stat.h>
-#endif  // _WIN32
 
 namespace google {
 namespace cloud {
@@ -224,14 +220,6 @@ std::string ServiceConfigYamlPath(
   return absl::StrCat(root, "/", name->second);
 }
 
-void MakeDirectory(std::string const& path) {
-#if _WIN32
-  _mkdir(path.c_str());
-#else
-  mkdir(path.c_str(), 0755);
-#endif  // _WIN32
-}
-
 void GenerateMetadata(
     std::map<std::string, std::string> const& vars,
     std::string const& output_path,
diff --git a/generator/internal/scaffold_generator.h b/generator/internal/scaffold_generator.h
index 2dce5c047f1ca..ae72bb64e0293 100644
--- a/generator/internal/scaffold_generator.h
+++ b/generator/internal/scaffold_generator.h
@@ -92,9 +92,6 @@ std::map<std::string, std::string> ScaffoldVars(
 std::string ServiceConfigYamlPath(
     std::string const& root, std::map<std::string, std::string> const& vars);
 
-/// Create a directory. The parent must exist.
-void MakeDirectory(std::string const& path);
-
 /**
  * Generates (if possible) a `.repo-metadata.json` file for @p service.
  *
diff --git a/generator/internal/scaffold_generator_test.cc b/generator/internal/scaffold_generator_test.cc
index b9b737ba19186..32b65820fc7d8 100644
--- a/generator/internal/scaffold_generator_test.cc
+++ b/generator/internal/scaffold_generator_test.cc
@@ -13,11 +13,17 @@
 // limitations under the License.
 
 #include "generator/internal/scaffold_generator.h"
+#include "generator/internal/codegen_utils.h"
 #include "google/cloud/internal/random.h"
 #include <gmock/gmock.h>
 #include <cstdlib>
 #include <fstream>
 #include <sstream>
+#if _WIN32
+#include <direct.h>
+#else
+#include <unistd.h>
+#endif  // _WIN32
 
 namespace google {
 namespace cloud {