diff --git a/internal/ceres/file.h b/internal/ceres/file.h
index 219b459..c0015df 100644
--- a/internal/ceres/file.h
+++ b/internal/ceres/file.h
@@ -34,18 +34,20 @@
 #define CERES_INTERNAL_FILE_H_
 
 #include <string>
+
 #include "ceres/internal/port.h"
 
 namespace ceres {
 namespace internal {
 
-void WriteStringToFileOrDie(const std::string &data,
-                            const std::string &filename);
-void ReadFileToStringOrDie(const std::string &filename, std::string *data);
+void WriteStringToFileOrDie(const std::string& data,
+                            const std::string& filename);
+void ReadFileToStringOrDie(const std::string& filename, std::string* data);
 
 // Join two path components, adding a slash if necessary.  If basename is an
 // absolute path then JoinPath ignores dirname and simply returns basename.
-std::string JoinPath(const std::string& dirname, const std::string& basename);
+CERES_EXPORT_INTERNAL std::string JoinPath(const std::string& dirname,
+                                           const std::string& basename);
 
 }  // namespace internal
 }  // namespace ceres