--- proc/sysinfo.c
+++ proc/sysinfo.c	2015-01-27 15:04:57.337518882 +0000
@@ -708,8 +708,14 @@ nextline:
   kb_main_cached = kb_page_cache + kb_slab;
   if ((ev=getenv("PS_FULL_CACHE")))
     kb_main_cached += kb_slab_reclaimable + kb_swap_cached + kb_nfs_unstable;
-  kb_swap_used = kb_swap_total - kb_swap_free;
-  kb_main_used = kb_main_total - kb_main_free - kb_main_cached - kb_main_buffers;
+  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_cached + kb_main_buffers)
+    kb_main_used = kb_main_total - kb_main_free - kb_main_cached - kb_main_buffers;
+  else
+    kb_main_used = 0;
 
   /* zero? might need fallback for 2.6.27 <= kernel <? 3.14 */
   if (!kb_main_available) {
--- free.c
+++ free.c	2015-01-27 15:07:36.725518136 +0000
@@ -327,15 +327,28 @@ 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(" %11s", scale_size(kb_low_total, flags, args));
-			printf(" %11s", scale_size(kb_low_total - kb_low_free, flags, args));
+			printf(" %11s", scale_size(kb_low_used, flags, args));
 			printf(" %11s", scale_size(kb_low_free, flags, args));
 			printf("\n");
 
 			printf("%-7s", _("High:"));
 			printf(" %11s", scale_size(kb_high_total, flags, args));
-			printf(" %11s", scale_size(kb_high_total - kb_high_free, flags, args));
+			printf(" %11s", scale_size(kb_high_used, flags, args));
 			printf(" %11s", scale_size(kb_high_free, flags, args));
 			printf("\n");
 		}