--- proc/sysinfo.c
+++ proc/sysinfo.c	2012-06-04 09:45:53.448364904 +0000
@@ -676,8 +676,16 @@ nextline:
   if(kb_inactive==~0UL){
     kb_inactive = kb_inact_dirty + kb_inact_clean + kb_inact_laundry;
   }
-  kb_swap_used = kb_swap_total - kb_swap_free;
-  kb_main_used = kb_main_total - kb_main_free;
+  if (kb_swap_total > kb_swap_free) {
+    kb_swap_used = kb_swap_total - kb_swap_free;
+  } else {
+    kb_swap_used = 0;
+  }
+  if (kb_main_total > kb_main_free) {
+    kb_main_used = kb_main_total - kb_main_free;
+  } else {
+    kb_main_used = 0;
+  }
   kb_main_cached += kb_swap_reclaimable + kb_swap_cached + kb_nfs_unstable;
 }
 
--- free.c
+++ free.c	2012-06-04 09:50:26.588010539 +0000
@@ -310,24 +310,44 @@ int main(int argc, char **argv)
 		 * to print the high info, even if it is zero.
 		 */
 		if (flags & FREE_LOHI) {
+			unsigned long kb_low_used;
+			unsigned long kb_high_used;
+
+			if (kb_low_total > kb_low_free)
+				kb_low_used = kb_low_total - kb_low_free;
+			else
+				kb_low_used = 0;
+
+			if (kb_high_total > kb_high_free)
+				kb_high_used = kb_high_total - kb_high_free;
+			else
+				kb_high_used = 0;
+
 			printf("%-7s", _("Low:"));
 			printf(" %10s", scale_size(kb_low_total, flags, args));
-			printf(" %10s", scale_size(kb_low_total - kb_low_free, flags, args));
+			printf(" %10s", scale_size(kb_low_used, flags, args));
 			printf(" %10s", scale_size(kb_low_free, flags, args));
 			printf("\n");
 
 			printf("%-7s", _("High:"));
 			printf(" %10s", scale_size(kb_high_total, flags, args));
-			printf(" %10s", scale_size(kb_high_total - kb_high_free, flags, args));
+			printf(" %10s", scale_size(kb_high_used, flags, args));
 			printf(" %10s", scale_size(kb_high_free, flags, args));
 			printf("\n");
 		}
 
 		if (!(flags & FREE_OLDFMT)) {
 			unsigned KLONG buffers_plus_cached = kb_main_buffers + kb_main_cached;
+			unsigned long kb_used_minus_bufcache;
+
+			if (kb_main_used > buffers_plus_cached)
+				kb_used_minus_bufcache = kb_main_used - buffers_plus_cached;
+			else
+				kb_used_minus_bufcache = 0;
+
 			printf(_("-/+ buffers/cache:"));
 			printf(" %10s",
-			       scale_size(kb_main_used - buffers_plus_cached, flags, args));
+			       scale_size(kb_used_minus_bufcache, flags, args));
 			printf(" %10s",
 			       scale_size(kb_main_free + buffers_plus_cached, flags, args));
 			printf("\n");