diff --git a/MANPAGE.md b/MANPAGE.md
index f7a4f1e..2e8e567 100644
--- a/MANPAGE.md
+++ b/MANPAGE.md
@@ -26,7 +26,7 @@ If there is a failure when trying to kill a process, **earlyoom** sleeps for
 # OPTIONS
 
 #### -m PERCENT[,KILL_PERCENT]
-set available memory minimum to PERCENT of total (default 10 %).
+set available memory minimum to PERCENT of MemAvailable+AnonPages (as reported in **/proc/meminfo**) at the time of initialization (default 10 %).
 
 earlyoom starts sending SIGTERM once **both** memory **and** swap are below their
 respective PERCENT setting. It sends SIGKILL once **both** are below their respective
diff --git a/main.c b/main.c
index 8540654..72a9bce 100644
--- a/main.c
+++ b/main.c
@@ -291,8 +291,8 @@ int main(int argc, char* argv[])
     }
     // Merge "-M" with "-m" values
     if (have_M) {
-        double M_term_percent = 100 * mem_term_kib / (double)m.MemTotalKiB;
-        double M_kill_percent = 100 * mem_kill_kib / (double)m.MemTotalKiB;
+        double M_term_percent = 100 * mem_term_kib / (double)m.UserMemTotalKiB;
+        double M_kill_percent = 100 * mem_kill_kib / (double)m.UserMemTotalKiB;
         if (have_m) {
             // Both -m and -M were passed. Use the lower of both values.
             args.mem_term_percent = min(args.mem_term_percent, M_term_percent);