diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0bf678ec8..6e51dc113 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -64,6 +64,9 @@ set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")
 set(CMAKE_CXX_FLAGS_GPROF          "-O2 -g -pg")
 
+include(CheckIncludeFileCXX)
+check_include_file_cxx("unistd.h" HAVE_UNISTD)
+
 # SPLIT_STACK
 if ("${SPLIT_STACK}" MATCHES "ON")
   if ((${CMAKE_SYSTEM_NAME} MATCHES "Linux") AND ("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU"))
diff --git a/src/util/lean_path.cpp b/src/util/lean_path.cpp
index 9a59fcdb2..01d8cc382 100644
--- a/src/util/lean_path.cpp
+++ b/src/util/lean_path.cpp
@@ -219,7 +219,7 @@ optional<std::string> check_file(std::string const & path, std::string const & f
         file += ext;
     std::ifstream ifile(file);
     if (ifile)
-        return optional<std::string>(realpath(file.c_str()));
+        return optional<std::string>(lrealpath(file.c_str()));
     else
         return optional<std::string>();
 }
diff --git a/src/util/realpath.cpp b/src/util/realpath.cpp
index d36e54ea0..e98843571 100644
--- a/src/util/realpath.cpp
+++ b/src/util/realpath.cpp
@@ -7,12 +7,13 @@ Author: Leonardo de Moura
 #include <string>
 #include <cstdlib>
 #include "util/realpath.h"
+
 #ifdef LEAN_WINDOWS
 #include <windows.h>
 #endif
 
 namespace lean {
-std::string realpath(char const * fname) {
+std::string lrealpath(char const * fname) {
 #ifdef LEAN_WINDOWS
     constexpr unsigned BufferSize = 8192;
     char buffer[BufferSize];
@@ -23,7 +24,7 @@ std::string realpath(char const * fname) {
         return std::string(buffer);
     }
 #else
-    char * tmp = ::realpath(fname, nullptr);
+    char * tmp = realpath(fname, nullptr);
     std::string r(tmp);
     free(tmp);
     return r;
diff --git a/src/util/realpath.h b/src/util/realpath.h
index c7c8735eb..5ebb164eb 100644
--- a/src/util/realpath.h
+++ b/src/util/realpath.h
@@ -7,5 +7,5 @@ Author: Leonardo de Moura
 #pragma once
 #include <string>
 namespace lean {
-std::string realpath(char const * fname);
+std::string lrealpath(char const * fname);
 }