diff --git a/psycopg/lobject.h b/psycopg/lobject.h
index b9c8c3d8..73cf6192 100644
--- a/psycopg/lobject.h
+++ b/psycopg/lobject.h
@@ -60,8 +60,8 @@ RAISES_NEG HIDDEN int lobject_export(lobjectObject *self, const char *filename);
 RAISES_NEG HIDDEN Py_ssize_t lobject_read(lobjectObject *self, char *buf, size_t len);
 RAISES_NEG HIDDEN Py_ssize_t lobject_write(lobjectObject *self, const char *buf,
                                 size_t len);
-RAISES_NEG HIDDEN long lobject_seek(lobjectObject *self, long pos, int whence);
-RAISES_NEG HIDDEN long lobject_tell(lobjectObject *self);
+RAISES_NEG HIDDEN Py_ssize_t lobject_seek(lobjectObject *self, Py_ssize_t pos, int whence);
+RAISES_NEG HIDDEN Py_ssize_t lobject_tell(lobjectObject *self);
 RAISES_NEG HIDDEN int lobject_truncate(lobjectObject *self, size_t len);
 RAISES_NEG HIDDEN int lobject_close(lobjectObject *self);
 
diff --git a/psycopg/lobject_int.c b/psycopg/lobject_int.c
index 6b55d42b..165af6c9 100644
--- a/psycopg/lobject_int.c
+++ b/psycopg/lobject_int.c
@@ -376,12 +376,12 @@ lobject_read(lobjectObject *self, char *buf, size_t len)
 
 /* lobject_seek - move the current position in the lo */
 
-RAISES_NEG long
-lobject_seek(lobjectObject *self, long pos, int whence)
+RAISES_NEG Py_ssize_t
+lobject_seek(lobjectObject *self, Py_ssize_t pos, int whence)
 {
     PGresult *pgres = NULL;
     char *error = NULL;
-    long where;
+    Py_ssize_t where;
 
     Dprintf("lobject_seek: fd = %d, pos = %ld, whence = %d",
             self->fd, pos, whence);
@@ -391,12 +391,12 @@ lobject_seek(lobjectObject *self, long pos, int whence)
 
 #ifdef HAVE_LO64
     if (self->conn->server_version < 90300) {
-        where = (long)lo_lseek(self->conn->pgconn, self->fd, (int)pos, whence);
+        where = (Py_ssize_t)lo_lseek(self->conn->pgconn, self->fd, (int)pos, whence);
     } else {
-        where = lo_lseek64(self->conn->pgconn, self->fd, pos, whence);
+        where = (Py_ssize_t)lo_lseek64(self->conn->pgconn, self->fd, pos, whence);
     }
 #else
-    where = (long)lo_lseek(self->conn->pgconn, self->fd, (int)pos, whence);
+    where = (Py_ssize_t)lo_lseek(self->conn->pgconn, self->fd, (int)pos, whence);
 #endif
     Dprintf("lobject_seek: where = %ld", where);
     if (where < 0)
@@ -412,12 +412,12 @@ lobject_seek(lobjectObject *self, long pos, int whence)
 
 /* lobject_tell - tell the current position in the lo */
 
-RAISES_NEG long
+RAISES_NEG Py_ssize_t
 lobject_tell(lobjectObject *self)
 {
     PGresult *pgres = NULL;
     char *error = NULL;
-    long where;
+    Py_ssize_t where;
 
     Dprintf("lobject_tell: fd = %d", self->fd);
 
@@ -426,12 +426,12 @@ lobject_tell(lobjectObject *self)
 
 #ifdef HAVE_LO64
     if (self->conn->server_version < 90300) {
-        where = (long)lo_tell(self->conn->pgconn, self->fd);
+        where = (Py_ssize_t)lo_tell(self->conn->pgconn, self->fd);
     } else {
-        where = lo_tell64(self->conn->pgconn, self->fd);
+        where = (Py_ssize_t)lo_tell64(self->conn->pgconn, self->fd);
     }
 #else
-    where = (long)lo_tell(self->conn->pgconn, self->fd);
+    where = (Py_ssize_t)lo_tell(self->conn->pgconn, self->fd);
 #endif
     Dprintf("lobject_tell: where = %ld", where);
     if (where < 0)
diff --git a/psycopg/lobject_type.c b/psycopg/lobject_type.c
index ec95b5cf..973ebe76 100644
--- a/psycopg/lobject_type.c
+++ b/psycopg/lobject_type.c
@@ -105,7 +105,7 @@ psyco_lobj_write(lobjectObject *self, PyObject *args)
         goto exit;
     }
 
-    rv = PyInt_FromLong((long)res);
+    rv = PyInt_FromSsize_t((Py_ssize_t)res);
 
 exit:
     Py_XDECREF(data);
@@ -121,7 +121,7 @@ static PyObject *
 psyco_lobj_read(lobjectObject *self, PyObject *args)
 {
     PyObject *res;
-    long where, end;
+    Py_ssize_t where, end;
     Py_ssize_t size = -1;
     char *buffer;
 
@@ -165,10 +165,10 @@ psyco_lobj_read(lobjectObject *self, PyObject *args)
 static PyObject *
 psyco_lobj_seek(lobjectObject *self, PyObject *args)
 {
-    long offset, pos=0;
+    Py_ssize_t offset, pos=0;
     int whence=0;
 
-    if (!PyArg_ParseTuple(args, "l|i", &offset, &whence))
+    if (!PyArg_ParseTuple(args, "n|i", &offset, &whence))
         return NULL;
 
     EXC_IF_LOBJ_CLOSED(self);
@@ -187,8 +187,8 @@ psyco_lobj_seek(lobjectObject *self, PyObject *args)
 #else
     if (offset < INT_MIN || offset > INT_MAX) {
         PyErr_Format(InterfaceError,
-            "offset out of range (%ld): this psycopg version was not built "
-            "with lobject 64 API support",
+            "offset out of range (" FORMAT_CODE_PY_SSIZE_T "): "
+            "this psycopg version was not built with lobject 64 API support",
             offset);
         return NULL;
     }
@@ -197,7 +197,7 @@ psyco_lobj_seek(lobjectObject *self, PyObject *args)
     if ((pos = lobject_seek(self, offset, whence)) < 0)
         return NULL;
 
-    return PyLong_FromLong(pos);
+    return PyLong_FromSsize_t(pos);
 }
 
 /* tell method - tell current position in the lobject */
@@ -208,7 +208,7 @@ psyco_lobj_seek(lobjectObject *self, PyObject *args)
 static PyObject *
 psyco_lobj_tell(lobjectObject *self, PyObject *args)
 {
-    long pos;
+    Py_ssize_t pos;
 
     EXC_IF_LOBJ_CLOSED(self);
     EXC_IF_LOBJ_LEVEL0(self);
@@ -217,7 +217,7 @@ psyco_lobj_tell(lobjectObject *self, PyObject *args)
     if ((pos = lobject_tell(self)) < 0)
         return NULL;
 
-    return PyLong_FromLong(pos);
+    return PyLong_FromSsize_t(pos);
 }
 
 /* unlink method - unlink (destroy) the lobject */
@@ -274,9 +274,9 @@ psyco_lobj_get_closed(lobjectObject *self, void *closure)
 static PyObject *
 psyco_lobj_truncate(lobjectObject *self, PyObject *args)
 {
-    long len = 0;
+    Py_ssize_t len = 0;
 
-    if (!PyArg_ParseTuple(args, "|l", &len))
+    if (!PyArg_ParseTuple(args, "|n", &len))
         return NULL;
 
     EXC_IF_LOBJ_CLOSED(self);
@@ -286,16 +286,16 @@ psyco_lobj_truncate(lobjectObject *self, PyObject *args)
 #ifdef HAVE_LO64
     if (len > INT_MAX && self->conn->server_version < 90300) {
         PyErr_Format(NotSupportedError,
-            "len out of range (%ld): server version %d "
-            "does not support the lobject 64 API",
+            "len out of range (" FORMAT_CODE_PY_SSIZE_T "): "
+            "server version %d does not support the lobject 64 API",
             len, self->conn->server_version);
         return NULL;
     }
 #else
     if (len > INT_MAX) {
         PyErr_Format(InterfaceError,
-            "len out of range (%ld): this psycopg version was not built "
-            "with lobject 64 API support",
+            "len out of range (" FORMAT_CODE_PY_SSIZE_T "): "
+            "this psycopg version was not built with lobject 64 API support",
             len);
         return NULL;
     }