diff --git a/ChangeLog b/ChangeLog
index 48ca30ee2..8814c2279 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2013-03-10  Vladimir Serbinenko  <phcoder@gmail.com>
+
+	* include/grub/datetime.h (grub_datetime2unixtime): Fix unixtime
+	computation for some years before epoch. Avode confusing division
+	while on it.
+
 2013-03-10  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	* grub-core/video/i386/pc/vbe.c
diff --git a/include/grub/datetime.h b/include/grub/datetime.h
index 3a3b3d0c3..fef281404 100644
--- a/include/grub/datetime.h
+++ b/include/grub/datetime.h
@@ -89,9 +89,7 @@ grub_datetime2unixtime (const struct grub_datetime *datetime, grub_int32_t *nix)
   ret = 3 * SECPERYEAR + SECPERDAY;
 
   /* Transform C divisions and modulos to mathematical ones */
-  y4 = (datetime->year - 1973) / 4;
-  if (datetime->year < 1973)
-    y4--;
+  y4 = ((datetime->year - 1) >> 2) - (1973 / 4);
   ay = datetime->year - 1973 - 4 * y4;
   ret += y4 * SECPER4YEARS;
   ret += ay * SECPERYEAR;