diff --git a/sys/platform/pc64/x86_64/mptable.c b/sys/platform/pc64/x86_64/mptable.c
index aaf8fd7f13..29334dda2b 100644
--- a/sys/platform/pc64/x86_64/mptable.c
+++ b/sys/platform/pc64/x86_64/mptable.c
@@ -283,7 +283,7 @@ mptable_search(void)
 			return x;
 	} else {
 		/* last 1K of base memory, effective 'top of base' passed in */
-		target = (u_int32_t)(base_memory - 0x400);
+		target = (u_int32_t)((base_memory * 1024) - 0x400);
 		if ((x = mptable_search_sig(target, 1024 / 4)) > 0)
 			return x;
 	}