diff --git a/Modules/timemodule.c b/Modules/timemodule.c
index b01366a..7d53179 100644
--- a/Modules/timemodule.c
+++ b/Modules/timemodule.c
@@ -41,6 +41,14 @@
 
 #ifdef macintosh
 #include <time.h>
+#include <OSUtils.h>
+#ifdef USE_GUSI2
+/* GUSI, the I/O library which has the time() function and such uses the
+** Mac epoch of 1904. MSL, the C library which has localtime() and so uses
+** the ANSI epoch of 1900.
+*/
+#define GUSI_TO_MSL_EPOCH (4*365*24*60*60)
+#endif /* USE_GUSI2 */
 #else
 #include <sys/types.h>
 #endif
@@ -271,6 +279,9 @@
 {
 	struct tm *p;
 	errno = 0;
+#if defined(macintosh) && defined(USE_GUSI2)
+	when = when + GUSI_TO_MSL_EPOCH;
+#endif
 	p = function(&when);
 	if (p == NULL) {
 #ifdef EINVAL
@@ -480,6 +491,9 @@
 	if (!PyArg_Parse(args, "d", &dt))
 		return NULL;
 	tt = (time_t)dt;
+#if defined(macintosh) && defined(USE_GUSI2)
+	tt = tt + GUSI_TO_MSL_EPOCH;
+#endif
 	p = ctime(&tt);
 	if (p == NULL) {
 		PyErr_SetString(PyExc_ValueError, "unconvertible time");
@@ -517,6 +531,9 @@
                                 "mktime argument out of range");
 		return NULL;
 	}
+#if defined(macintosh) && defined(USE_GUSI2)
+	tt = tt - GUSI_TO_MSL_EPOCH;
+#endif
 	return PyFloat_FromDouble((double)tt);
 }