diff --git a/lang/mono/Makefile b/lang/mono/Makefile
index 36f548b4946..a235fb882da 100644
--- a/lang/mono/Makefile
+++ b/lang/mono/Makefile
@@ -1,4 +1,4 @@
-# $OpenBSD: Makefile,v 1.39 2010/04/08 16:40:04 robert Exp $
+# $OpenBSD: Makefile,v 1.40 2010/04/16 11:59:45 robert Exp $
 
 # sync with net/avahi,-mono
 ONLY_FOR_ARCHS=	amd64 i386 powerpc # arm
@@ -6,7 +6,7 @@ ONLY_FOR_ARCHS=	amd64 i386 powerpc # arm
 COMMENT=	cross platform, open source .NET developement framework
 
 DISTNAME=	mono-2.6.3
-PKGNAME=	${DISTNAME}p17
+PKGNAME=	${DISTNAME}p18
 
 CATEGORIES=	lang devel
 
diff --git a/lang/mono/patches/patch-mono_io-layer_collection_c b/lang/mono/patches/patch-mono_io-layer_collection_c
new file mode 100644
index 00000000000..4dd3cac3321
--- /dev/null
+++ b/lang/mono/patches/patch-mono_io-layer_collection_c
@@ -0,0 +1,12 @@
+$OpenBSD: patch-mono_io-layer_collection_c,v 1.1 2010/04/16 11:59:45 robert Exp $
+--- mono/io-layer/collection.c.orig	Fri Apr 16 11:26:15 2010
++++ mono/io-layer/collection.c	Fri Apr 16 11:26:24 2010
+@@ -60,7 +60,7 @@ void _wapi_collection_init (void)
+ 
+ #ifdef HAVE_PTHREAD_ATTR_SETSTACKSIZE
+         if (set_stacksize == 0) {
+-#if defined(__FreeBSD__) || defined(__NetBSD__)
++#if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__)
+                 ret = pthread_attr_setstacksize (&attr, 65536);
+ #else
+                 ret = pthread_attr_setstacksize (&attr, PTHREAD_STACK_MIN);
diff --git a/lang/mono/patches/patch-mono_metadata_boehm-gc_c b/lang/mono/patches/patch-mono_metadata_boehm-gc_c
new file mode 100644
index 00000000000..b5a5adff4ff
--- /dev/null
+++ b/lang/mono/patches/patch-mono_metadata_boehm-gc_c
@@ -0,0 +1,21 @@
+$OpenBSD: patch-mono_metadata_boehm-gc_c,v 1.1 2010/04/16 11:59:45 robert Exp $
+--- mono/metadata/boehm-gc.c.orig	Fri Apr 16 11:24:54 2010
++++ mono/metadata/boehm-gc.c	Fri Apr 16 11:26:01 2010
+@@ -84,6 +84,17 @@ mono_gc_base_init (void)
+ 	}
+ #elif defined(HAVE_PTHREAD_GET_STACKSIZE_NP) && defined(HAVE_PTHREAD_GET_STACKADDR_NP)
+ 		GC_stackbottom = (char*)pthread_get_stackaddr_np (pthread_self ());
++#elif defined(__OpenBSD__)
++#  include <pthread_np.h>
++	{
++		stack_t ss;
++		int rslt;
++
++		rslt = pthread_stackseg_np(pthread_self(), &ss);
++		g_assert (rslt == 0);
++
++		GC_stackbottom = (char*)ss.ss_sp;
++	}
+ #else
+ 	{
+ 		int dummy;