diff --git a/doc/Changelog b/doc/Changelog
index c7d09cbb6..f5861eb98 100644
--- a/doc/Changelog
+++ b/doc/Changelog
@@ -3,6 +3,7 @@
 	  modules can compute the response time.
 	- For #391: use struct timeval* start_time for callback information.
 	- For #391: fix indentation.
+	- For #391: more double casts in python start time calculation.
 
 6 January 2021: Wouter
 	- Fix #379: zone loading over HTTP appears to have buffer issues.
diff --git a/pythonmod/interface.i b/pythonmod/interface.i
index 6e629fa70..5dae04aa4 100644
--- a/pythonmod/interface.i
+++ b/pythonmod/interface.i
@@ -1548,7 +1548,7 @@ int edns_opt_list_append(struct edns_option** list, uint16_t code, size_t len,
         PyObject *py_rep, *py_repinfo, *py_region;
         PyObject *py_args, *py_kwargs, *result;
         int res = 0;
-        double py_start_time = start_time->tv_sec + start_time->tv_usec / 1e6;
+        double py_start_time = ((double)start_time->tv_sec) + ((double)start_time->tv_usec) / 1.0e6;
 
         PyGILState_STATE gstate = PyGILState_Ensure();
         func = (PyObject *) python_callback;