diff --git a/blockcheck2.d/standard/25-fake.sh b/blockcheck2.d/standard/25-fake.sh
index ef9de2e..e30af80 100644
--- a/blockcheck2.d/standard/25-fake.sh
+++ b/blockcheck2.d/standard/25-fake.sh
@@ -40,7 +40,7 @@ pktws_check_http()
 		for ff in $fake 0x00000000; do
 			pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=fake_http:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS && ok=1
 			# duplicate SYN with MD5
-			contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --payload=empty "--out-range=<s1" --lua-desync=send:tcp_md5 && ok=1
+			contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --payload=empty "--out-range=<s1" --lua-desync=send:$TCP_MD5 && ok=1
 		done
 	done
 	for ttl in $attls; do
@@ -76,7 +76,7 @@ pktws_fake_https_vary()
 	pktws_fake_https_vary_ "$1" "$2" "$3" "$4" "$5" && ok_any=1
 	# duplicate SYN with MD5
 	contains "$fooling" tcp_md5 && \
-		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:tcp_md5" && ok_any=1
+		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:$TCP_MD5" && ok_any=1
 	[ "$ok_any" = 1 ]
 }
 
diff --git a/blockcheck2.d/standard/30-faked.sh b/blockcheck2.d/standard/30-faked.sh
index 54f4514..3956dfe 100644
--- a/blockcheck2.d/standard/30-faked.sh
+++ b/blockcheck2.d/standard/30-faked.sh
@@ -42,7 +42,7 @@ pktws_check_faked()
 			for split in $splits; do
 				pktws_curl_test_update $testf $domain ${FAKED_PATTERN:+--blob=faked_pat:@"$FAKED_PATTERN" }$pre $PAYLOAD --lua-desync=$splitf:${FAKED_PATTERN:+pattern=faked_pat:}pos=$split:$fooling && ok=1
 				# duplicate SYN with MD5
-				contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKED_PATTERN:+--blob=faked_pat:@"$FAKED_PATTERN" }$pre $PAYLOAD --lua-desync=$splitf:${FAKED_PATTERN:+pattern=faked_pat:}pos=$split:$fooling:repeats=$FAKE_REPEATS --payload=empty --out-range="<s1" --lua-desync=send:tcp_md5 && ok=1
+				contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKED_PATTERN:+--blob=faked_pat:@"$FAKED_PATTERN" }$pre $PAYLOAD --lua-desync=$splitf:${FAKED_PATTERN:+pattern=faked_pat:}pos=$split:$fooling:repeats=$FAKE_REPEATS --payload=empty --out-range="<s1" --lua-desync=send:$TCP_MD5 && ok=1
 			done
 		done
 		for ttl in $attls; do
diff --git a/blockcheck2.d/standard/35-hostfake.sh b/blockcheck2.d/standard/35-hostfake.sh
index 5c816c9..fc635eb 100644
--- a/blockcheck2.d/standard/35-hostfake.sh
+++ b/blockcheck2.d/standard/35-hostfake.sh
@@ -21,7 +21,7 @@ pktws_hostfake_vary()
 	pktws_hostfake_vary_ "$1" "$2" "$3" "$4" "$5" && ok_any=1
 	# duplicate SYN with MD5
 	contains "$fooling" tcp_md5 && \
-		pktws_hostfake_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:tcp_md5" && ok_any=1
+		pktws_hostfake_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:$TCP_MD5" && ok_any=1
 	[ "$ok_any" = 1 ]
 }
 
diff --git a/blockcheck2.d/standard/50-fake-multi.sh b/blockcheck2.d/standard/50-fake-multi.sh
index f879321..cc092fe 100644
--- a/blockcheck2.d/standard/50-fake-multi.sh
+++ b/blockcheck2.d/standard/50-fake-multi.sh
@@ -46,7 +46,7 @@ pktws_check_http()
 				for ff in $fake 0x00000000; do
 					pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:pos=$split && ok=1
 					# duplicate SYN with MD5
-					contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=fake_http:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:pos=$split --payload=empty "--out-range=<s1" --lua-desync=send:tcp_md5 && ok=1
+					contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=fake_http:@"$FAKE_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:pos=$split --payload=empty "--out-range=<s1" --lua-desync=send:$TCP_MD5 && ok=1
 				done
 			done
 		done
@@ -82,7 +82,7 @@ pktws_fake_https_vary()
 	pktws_fake_https_vary_ "$1" "$2" "$3" "$4" "$5" && ok_any=1
 	# duplicate SYN with MD5
 	contains "$fooling" tcp_md5 && \
-		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:tcp_md5" && ok_any=1
+		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:$TCP_MD5" && ok_any=1
 	[ "$ok_any" = 1 ]
 }
 
diff --git a/blockcheck2.d/standard/55-fake-faked.sh b/blockcheck2.d/standard/55-fake-faked.sh
index 8c903ff..496e3f5 100644
--- a/blockcheck2.d/standard/55-fake-faked.sh
+++ b/blockcheck2.d/standard/55-fake-faked.sh
@@ -46,7 +46,7 @@ pktws_check_http()
 				for ff in $fake 0x00000000; do
 					pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }${FAKED_PATTERN_HTTP:+--blob=faked_pat:@"$FAKED_PATTERN_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:${FAKED_PATTERN_HTTP:+pattern=faked_pat:}pos=$split:$fooling:repeats=$FAKE_REPEATS && ok=1
 					# duplicate SYN with MD5
-					contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }${FAKED_PATTERN_HTTP:+--blob=faked_pat:@"$FAKED_PATTERN_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:${FAKED_PATTERN_HTTP:+pattern=faked_pat:}pos=$split:$fooling:repeats=$FAKE_REPEATS --payload=empty "--out-range=<s1" --lua-desync=send:tcp_md5 && ok=1
+					contains "$fooling" tcp_md5 && pktws_curl_test_update $testf $domain ${FAKE_HTTP:+--blob=$fake:@"$FAKE_HTTP" }${FAKED_PATTERN_HTTP:+--blob=faked_pat:@"$FAKED_PATTERN_HTTP" }$PAYLOAD --lua-desync=fake:blob=$ff:$fooling:repeats=$FAKE_REPEATS --lua-desync=$splitf:${FAKED_PATTERN_HTTP:+pattern=faked_pat:}pos=$split:$fooling:repeats=$FAKE_REPEATS --payload=empty "--out-range=<s1" --lua-desync=send:$TCP_MD5 && ok=1
 				done
 			done
 		done
@@ -83,7 +83,7 @@ pktws_fake_https_vary()
 	pktws_fake_https_vary_ "$1" "$2" "$3" "$4" "$5" && ok_any=1
 	# duplicate SYN with MD5
 	contains "$fooling" tcp_md5 && \
-		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:tcp_md5" && ok_any=1
+		pktws_fake_https_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:$TCP_MD5" && ok_any=1
 	[ "$ok_any" = 1 ]
 }
 
diff --git a/blockcheck2.d/standard/60-fake-hostfake.sh b/blockcheck2.d/standard/60-fake-hostfake.sh
index 1b2d32e..9551434 100644
--- a/blockcheck2.d/standard/60-fake-hostfake.sh
+++ b/blockcheck2.d/standard/60-fake-hostfake.sh
@@ -20,7 +20,7 @@ pktws_hostfake_vary()
 	pktws_hostfake_vary_ "$1" "$2" "$3" "$4" "$5"
 	# duplicate SYN with MD5
 	contains "$fooling" tcp_md5 && \
-		pktws_hostfake_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:tcp_md5"
+		pktws_hostfake_vary_  "$1" "$2" "$3" "$4" "${5:+$5 }--payload=empty --out-range=<s1 --lua-desync=send:$TCP_MD5"
 }
 
 pktws_check_hostfake()
diff --git a/blockcheck2.d/standard/def.inc b/blockcheck2.d/standard/def.inc
index 593ee8a..893e059 100644
--- a/blockcheck2.d/standard/def.inc
+++ b/blockcheck2.d/standard/def.inc
@@ -15,3 +15,7 @@ MAX_AUTOTTL_DELTA=${MAX_AUTOTTL_DELTA:-5}
 
 # can use MULTIDISORER=multidisorder_legacy
 MULTIDISORDER=${MULTIDISORDER:-multidisorder}
+
+TCP_MD5=tcp_md5
+# OpenBSD can occupy 24 bytes in tcp options in SYN packet leaving no space for the md5 header
+[ "$UNAME" = OpenBSD ] && TCP_MD5=$TCP_MD5:tcp_nop_del