diff --git a/src/port/gettimeofday.c b/src/port/gettimeofday.c
index ab4f491..f4d8393 100644
--- a/src/port/gettimeofday.c
+++ b/src/port/gettimeofday.c
@@ -35,6 +35,13 @@
 static const unsigned __int64 epoch = UINT64CONST(116444736000000000);
 
 /*
+ * FILETIME represents the number of 100-nanosecond intervals since
+ * January 1, 1601 (UTC).
+ */
+#define FILETIME_PER_SEC	10000000L
+#define FILETIME_PER_USEC	10
+
+/*
  * Both GetSystemTimeAsFileTime and GetSystemTimePreciseAsFileTime share a
  * signature, so we can just store a pointer to whichever we find. This
  * is the pointer's type.
@@ -98,8 +105,9 @@ gettimeofday(struct timeval * tp, struct timezone * tzp)
 	ularge.LowPart = file_time.dwLowDateTime;
 	ularge.HighPart = file_time.dwHighDateTime;
 
-	tp->tv_sec = (long) ((ularge.QuadPart - epoch) / 10000000L);
-	tp->tv_usec = (long) (((ularge.QuadPart - epoch) % 10000000L) / 10);
+	tp->tv_sec = (long) ((ularge.QuadPart - epoch) / FILETIME_PER_SEC);
+	tp->tv_usec = (long) (((ularge.QuadPart - epoch) % FILETIME_PER_SEC)
+		/ FILETIME_PER_USEC);
 
 	return 0;
 }