diff --git a/CHANGELOG b/CHANGELOG
index 70b5b0aa3..0332b8a04 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -34,12 +34,15 @@ o Fixed a traceroute bug related to tracing between interfaces of a
   multi-homed host.  Thanks to David Fifield for reporting the problem
   and Eddie Bell for the fix.
 
-o Service detection (-sV) is now disabled when used with the IPProto Scan
-  (-sO).  Nmap would try to run the Service Scan after the IPProto Scan,
-  which would cause it to fail without outputting the protocol information,
-  or performing any other tasks (like Traceroute).  The Service Detection
-  line informing you where to send incorrect results is no longer outputted
-  when using the Service Scan with the Ping Scan (-sP) either. [Kris]
+o Service detection (-sV) and OS detection (-O) are now disabled when used
+  with the IPProto Scan (-sO).  When Nmap would try to run the Service Scan
+  after the IPProto Scan, it would cause it to fail without outputting the
+  protocol information, or performing any other tasks (like Traceroute).
+  When trying to perform OS detection, it would use the protocol information
+  it got from the IPProto Scan to try to get the port numbers to use.  The
+  Service Detection line informing you where to send incorrect results is
+  no longer outputted when using the Service Scan with the Ping Scan (-sP)
+  either. [Kris]
 
 o Updated IANA assignment IP list for random IP (-iR) generation. [Kris]
 
diff --git a/NmapOps.cc b/NmapOps.cc
index 36bf3f9a1..0f3ef8a02 100644
--- a/NmapOps.cc
+++ b/NmapOps.cc
@@ -437,6 +437,11 @@ void NmapOps::ValidateOptions() {
     fatal("WARNING:  OS Scan is unreliable with a ping scan.  You need to use a scan type along with it, such as -sS, -sT, -sF, etc instead of -sP");
   }
 
+  if (osscan && ipprotscan) {
+    error("WARNING: Disabling OS Scan (-O) as it is incompatible with the IPProto Scan (-sO)");
+    osscan = 0;
+  }
+
   if (servicescan && ipprotscan) {
     error("WARNING: Disabling Service Scan (-sV) as it is incompatible with the IPProto Scan (-sO)");
     servicescan = 0;