diff --git a/src/if_py_both.h b/src/if_py_both.h
index 681b7a1..eca07ae 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -2394,6 +2394,9 @@
     if (end == -1)
 	end = self->buf->b_ml.ml_line_count;
 
+    if (n < 0)
+	n += end - start + 1;
+
     if (n < 0 || n > end - start)
     {
 	PyErr_SetString(PyExc_IndexError, _("line number out of range"));
@@ -2441,6 +2444,9 @@
     if (end == -1)
 	end = self->buf->b_ml.ml_line_count;
 
+    if (n < 0)
+	n += end - start + 1;
+
     if (n < 0 || n > end - start)
     {
 	PyErr_SetString(PyExc_IndexError, _("line number out of range"));