diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index d6c46e5..d12f980 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -4529,6 +4529,14 @@ int main(int argc, char* argv[])
         exit(EXIT_FAILURE);
     }
 
+    // mutex for basename/dirname
+    if(!init_basename_lock()){
+        S3FS_PRN_EXIT("could not initialize mutex for basename/dirname.");
+        s3fs_destroy_global_ssl();
+        destroy_parser_xml_lock();
+        exit(EXIT_FAILURE);
+    }
+
     // init curl (without mime types)
     //
     // [NOTE]
@@ -4549,6 +4557,7 @@ int main(int argc, char* argv[])
         S3FS_PRN_EXIT("Could not initiate curl library.");
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4563,6 +4572,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4579,6 +4589,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
     if(!S3fsCurl::FinalCheckSse()){
@@ -4586,6 +4597,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4605,6 +4617,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4619,6 +4632,7 @@ int main(int argc, char* argv[])
             S3fsCurl::DestroyS3fsCurl();
             s3fs_destroy_global_ssl();
             destroy_parser_xml_lock();
+            destroy_basename_lock();
             exit(EXIT_FAILURE);
         }
     }
@@ -4629,6 +4643,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4638,6 +4653,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4681,6 +4697,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(exitcode);
     }
 
@@ -4695,6 +4712,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4704,6 +4722,7 @@ int main(int argc, char* argv[])
         S3fsCurl::DestroyS3fsCurl();
         s3fs_destroy_global_ssl();
         destroy_parser_xml_lock();
+        destroy_basename_lock();
         exit(EXIT_FAILURE);
     }
 
@@ -4764,6 +4783,7 @@ int main(int argc, char* argv[])
     }
     s3fs_destroy_global_ssl();
     destroy_parser_xml_lock();
+    destroy_basename_lock();
 
     // cleanup xml2
     xmlCleanupParser();
diff --git a/src/s3fs_util.cpp b/src/s3fs_util.cpp
index 2a9d27e..23a2c7f 100644
--- a/src/s3fs_util.cpp
+++ b/src/s3fs_util.cpp
@@ -37,6 +37,7 @@
 #include "s3fs_util.h"
 #include "string_util.h"
 #include "s3fs_help.h"
+#include "autolock.h"
 
 //-------------------------------------------------------------------
 // Global variables
@@ -170,8 +171,60 @@ int is_uid_include_group(uid_t uid, gid_t gid)
 //-------------------------------------------------------------------
 // Utility for file and directory
 //-------------------------------------------------------------------
+// [NOTE]
+// basename/dirname returns a static variable pointer as the return value.
+// Normally this shouldn't be a problem, but in macos10 we found a case
+// where dirname didn't receive its return value correctly due to thread
+// conflicts.
+// To avoid this, exclusive control is performed by mutex.
+//
+static pthread_mutex_t* pbasename_lock = NULL;
+
+bool init_basename_lock()
+{
+    if(pbasename_lock){
+        S3FS_PRN_ERR("already initialized mutex for posix dirname/basename function.");
+        return false;
+    }
+    pbasename_lock = new pthread_mutex_t;
+
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+
+#if S3FS_PTHREAD_ERRORCHECK
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
+#endif
+    int result;
+    if(0 != (result = pthread_mutex_init(pbasename_lock, &attr))){
+        S3FS_PRN_ERR("failed to init pbasename_lock: %d.", result);
+        delete pbasename_lock;
+        pbasename_lock = NULL;
+        return false;
+    }
+    return true;
+}
+
+bool destroy_basename_lock()
+{
+    if(!pbasename_lock){
+        S3FS_PRN_ERR("the mutex for posix dirname/basename function is not initialized.");
+        return false;
+    }
+    int result;
+    if(0 != (result = pthread_mutex_destroy(pbasename_lock))){
+        S3FS_PRN_ERR("failed to destroy pbasename_lock: %d", result);
+        return false;
+    }
+    delete pbasename_lock;
+    pbasename_lock = NULL;
+
+    return true;
+}
+
 std::string mydirname(const std::string& path)
 {
+    AutoLock auto_lock(pbasename_lock);
+
     return std::string(dirname(const_cast<char*>(path.c_str())));
 }
 
@@ -187,6 +240,8 @@ std::string mydirname(const char* path)
 
 std::string mybasename(const std::string& path)
 {
+    AutoLock auto_lock(pbasename_lock);
+
     return std::string(basename(const_cast<char*>(path.c_str())));
 }
 
diff --git a/src/s3fs_util.h b/src/s3fs_util.h
index 5d0757d..243548e 100644
--- a/src/s3fs_util.h
+++ b/src/s3fs_util.h
@@ -40,6 +40,8 @@ void init_sysconf_vars();
 std::string get_username(uid_t uid);
 int is_uid_include_group(uid_t uid, gid_t gid);
 
+bool init_basename_lock();
+bool destroy_basename_lock();
 std::string mydirname(const char* path);
 std::string mydirname(const std::string& path);
 std::string mybasename(const char* path);