diff --git a/src/python-codec.c b/src/python-codec.c
index d94d9a6..ab81310 100644
--- a/src/python-codec.c
+++ b/src/python-codec.c
@@ -236,7 +236,7 @@ static PyObject *py_hdr_encode(PyObject *self, PyObject *args) {
     for (index=0; index < max_index;) {
         uint64_t value = get_entry(vsrc, index);
         ++index;
-         
+
         /* max encodable value must fit in 63 bit */
         if (value == 0) {
             int64_t zeros = 1;
@@ -269,7 +269,7 @@ static PyObject *py_hdr_encode(PyObject *self, PyObject *args) {
  */
 static PyObject *py_hdr_decode(PyObject *self, PyObject *args) {
     uint8_t *src;   /* t#: read only character buffer */
-    int src_len;    /*     its length */
+    Py_ssize_t src_len;    /*     its length */
     int read_index; /* i: start decoding from this offset, must be < src_len */
     void *vdst;     /* l: address of a counts array */
     int max_index;  /* i: number of entries in that array, must be > 0 */
@@ -380,7 +380,7 @@ static PyObject *py_hdr_add_array(PyObject *self, PyObject *args) {
     int max_index;  /* i: entries from 0 to max_index-1 are added */
     int word_size;  /* i: size of each entry in bytes 2,4,8 */
     uint64_t total_count = 0;
-    
+
     if (!PyArg_ParseTuple(args, "llii", &vdst, &vsrc, &max_index, &word_size)) {
         return NULL;
     }
diff --git a/src/python-codec.h b/src/python-codec.h
index 50cded7..629d922 100644
--- a/src/python-codec.h
+++ b/src/python-codec.h
@@ -1,4 +1,6 @@
 
+/* see https://python.readthedocs.io/en/stable/c-api/arg.html#strings-and-buffers */
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 
 static PyObject *py_hdr_encode(PyObject *self, PyObject *args);
diff --git a/test/raphael.hlog b/test/raphael.hlog
new file mode 100644
index 0000000..6969bf1
--- /dev/null
+++ b/test/raphael.hlog
@@ -0,0 +1,4 @@
+#[Histogram log format version 1.1]
+#[StartTime: 1629447481.658 (seconds since epoch), Fri Aug 20 08:18:01 UTC 2021]
+"StartTimestamp","Interval_Length","Interval_Max","Interval_Compressed_Histogram"
+1629447418.475,63.182,189.792,HISTggAABHJ42u2az6tNURTH969z733P9dz3w+/nN3mRCGVATIykFKFMDJQfA2LCQAbKH+BXTA0MDIiZgQyV/AMGRBlImUiUgXrS/R5l1Wqtfc553sP6Du6ns8/eZ++99l5r/+iOX7lx2bmD91xfAfQ/f+ZMTk7u+uRMJpPJZDKZTCaTyWQymUwmk8lkMplMJpPJZDKZTCaTyTTz5Bv+jq/4fVo+kfeBkCqS99xzQerh3gfm++X7QbANtsA55P0QOErezwMXk+cF4DpwC7gB3A7uBg+Bx8Gz4EXwMngLfAQ+Br/CHLC3XwRuBY+Cp2GGmxiebTDHmd/N0LmE7p/ss3sf3V7V5/BVmGMN+K7PMbR77E2fc9H/sffgM+S/1ucI2j+CfMNL++ydQn27YP4O2vEFfA0iffBDnwMv0P7P4Cv06zyG9zvYAzFexQrY4xsIe6dx2OsjiPSI9gakh6fgbfAAeAREfo92+SfgAxD28Oi3PwwuASdAzHeP9ru3hC/B5+BdEPW5h2D5P9E7JB/G1V0HL4DnQNjRnSTzE/10J8Bj4B5wP7iPpO8l/rCT+EXpLzvAjeBmcBO4GlwLYp665eB64pcTpFyZbxnhclIOfuXGyfMo8f/5hKNMehlHxgjnM/Gm5Ag4DHZJ+ixwLmnXbPL9leBCsEfy90i9Q+S5S9JpPB0iLOvvMHGXlh8k+QPpH30uyPc6THoi6W2yPiRmXWkx6ZGsR9w61CbPBbMOBqY9iWlfUrY/MuuwZ9bTwKR7oZxj7BGYdjlmXY/Cd0PmfsQzdvTKcoEZJ84+julnFPI75Xe1+0BuP8bNO25fFpV217bXKeePlk75PlYsl6tQcbykfL5meVez3qbPHVXPJTPl3BUyx8k3PE51z3O5fuWU/W5qvlUd/6hct6rGUy6+h4bq0cYVqb6gnLe589RPUdypWn6mxYc/3e/Y8PqRGyekfZK0LwjCvU7I9K+ojF+589sr+1HVnlp/zY0XueMZlHFE2l+FmvbKPX94YR3Q1hNr+k2uv4Sa884r44PkR1w+7txUKPsj7bu5c7M0H6V+BYFROQ9C5rhJ59Sq8SzVjEchMy7U3WdSP0o1zy9B6b/S/K7rx02f6yT7SN8NynRfMS5q73mSMh6lzHq1462N76nifKt77q+7z8g9z0nrohfiIjeuIbPfviF75PpZaNhPc+NAzCwXM+0g7fek86r2fixkjnNQtq/ufYKvOG5RGXeSMp+v6R/TdX40mUz/vqb6vq5phYb69bfY/3+ZZ03bIynP70l5DxCF8onZP0j7qSScv5KwH+LuIwqmvsDcz2jv1aKwf5Xunad7/vnMODJV8dT/p/7ddPmWUF76P0si3xkA20y+cl53SP4ueW4Rdhg/5O5RE2lHm/gtF3+k+08nnN86pN30/1i0voIwMXGmQ9hWxumCqa/FfCc0FH98w+WqxpuYua5UbS+dL20yXuX/Cun/73okvUuey/8FzmbmMbd+FsK6QsffC+u/Y9ZFJ6yXcZrj4q/2/ADzb0W5