diff --git a/setup.py b/setup.py
index 90b0a5a..6fe8b0f 100755
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,7 @@ def read(fname):
 
 setup(
     name = 'pyminizip',
-    version = '0.2.4',
+    version = '0.2.4.1',
     description = 'A minizip wrapper - To create a password encrypted zip file in python.',
     author='Shin Aoyama',
     author_email = "smihica@gmail.com",
diff --git a/src/py_minizip.c b/src/py_minizip.c
index 99d25b1..c67d232 100644
--- a/src/py_minizip.c
+++ b/src/py_minizip.c
@@ -319,8 +319,14 @@ int _compress(const char** srcs, int src_num, const char** srcspath, int srcpath
                         slash = &default_slash;
                     }
                 }
-                if (savefilepathnameinzip[filepathname_len-1] != *slash)
-                    extra_len = 1;
+
+                /* NOTE:
+                    don't add slash if filepathname_len is zero (prefix is an empty string)
+                    and avoid memory access violation */
+                if (filepathname_len > 0) {
+                    if (savefilepathnameinzip[filepathname_len-1] != *slash)
+                        extra_len = 1;
+                }
                 /* allocate buffer */
                 fullpathfileinzip = (char *)malloc(filename_len + filepathname_len + extra_len + 1);
                 if (fullpathfileinzip == NULL) {