--- nmap/docs/nmap-man.xml
+++ nmap/docs/nmap-man.xml
@@ -175,9 +175,9 @@ SERVICE/VERSION DETECTION:
   --version-all: Try every single probe (intensity 9)
   --version-trace: Show detailed version scan activity (for debugging)
 OS DETECTION:
-  -O: Enable OS detection (try 2nd generation w/fallback to 1st)
-  -O2: Only use the new OS detection system (no fallback)
-  -O1: Only use the old (1st generation) OS detection system
+  -O, -O1: Use the old (1st generation) OS detection system
+  -O2: Use the new (2nd generation) OS detection system
+  -O9: Enable OS detection (try 2nd generation w/fallback to 1st)
   --osscan-limit: Limit OS detection to promising targets
   --osscan-guess: Guess OS more aggressively
 TIMING AND PERFORMANCE:
--- nmap/docs/nmap.1
+++ nmap/docs/nmap.1
@@ -129,9 +129,9 @@ SERVICE/VERSION DETECTION:
   \-\-version\-all: Try every single probe (intensity 9)
   \-\-version\-trace: Show detailed version scan activity (for debugging)
 OS DETECTION:
-  \-O: Enable OS detection (try 2nd generation w/fallback to 1st)
-  \-O2: Only use the new OS detection system (no fallback)
-  \-O1: Only use the old (1st generation) OS detection system
+  \-O, \-O1: Use the old (1st generation) OS detection system
+  \-O2: Use the new (2nd generation) OS detection system
+  \-O9: Enable OS detection (try 2nd generation w/fallback to 1st)
   \-\-osscan\-limit: Limit OS detection to promising targets
   \-\-osscan\-guess: Guess OS more aggressively
 TIMING AND PERFORMANCE:
--- nmap/docs/nmap.usage.txt
+++ nmap/docs/nmap.usage.txt
@@ -36,9 +36,9 @@ SERVICE/VERSION DETECTION:
   --version-all: Try every single probe (intensity 9)
   --version-trace: Show detailed version scan activity (for debugging)
 OS DETECTION:
-  -O: Enable OS detection (try 2nd generation w/fallback to 1st)
-  -O2: Only use the new OS detection system (no fallback)
-  -O1: Only use the old (1st generation) OS detection system
+  -O, -O1: Use the old (1st generation) OS detection system
+  -O2: Use the new (2nd generation) OS detection system
+  -O9: Enable OS detection (try 2nd generation w/fallback to 1st)
   --osscan-limit: Limit OS detection to promising targets
   --osscan-guess: Guess OS more aggressively
 TIMING AND PERFORMANCE:
--- nmap/nmap.cc
+++ nmap/nmap.cc
@@ -225,9 +225,9 @@ printf("%s %s ( %s )\n"
        "  --version-all: Try every single probe (intensity 9)\n"
        "  --version-trace: Show detailed version scan activity (for debugging)\n"
        "OS DETECTION:\n"
-       "  -O: Enable OS detection (try 2nd generation w/fallback to 1st)\n"
-       "  -O2: Only use the new OS detection system (no fallback)\n"
-       "  -O1: Only use the old (1st generation) OS detection system\n"
+       "  -O, -O1: Use the old (1st generation) OS detection system\n"
+       "  -O2: Use the new (2nd generation) OS detection system\n"
+       "  -O9: Enable OS detection (try 2nd generation w/fallback to 1st)\n"
        "  --osscan-limit: Limit OS detection to promising targets\n"
        "  --osscan-guess: Guess OS more aggressively\n"
        "TIMING AND PERFORMANCE:\n"
@@ -809,7 +809,7 @@ int nmap_main(int argc, char *argv[]) {
     case 'A':
       o.servicescan = true;
       if (o.isr00t)
-		o.osscan = OS_SCAN_DEFAULT;
+		o.osscan = OS_SCAN_SYS_1_ONLY;
       break;
     case 'b': 
       o.bouncescan++;
@@ -889,11 +889,13 @@ int nmap_main(int argc, char *argv[]) {
     case 'n': o.noresolve++; break;
     case 'O': 
       if (!optarg)
-		o.osscan = OS_SCAN_DEFAULT;
+		o.osscan = OS_SCAN_SYS_1_ONLY;
       else if (*optarg == '1')
 		o.osscan = OS_SCAN_SYS_1_ONLY;
 	  else if (*optarg == '2')
 		o.osscan = OS_SCAN_SYS_2_ONLY;
+	  else if (*optarg == '9')
+		o.osscan = OS_SCAN_DEFAULT;
       else {
 	fatal("Use -O for new osscan engine, -O1 for old osscan engine.");
       }