diff --git a/building/linux64ARMv8/squeak.cog.spur/build.debug/mvm b/building/linux64ARMv8/squeak.cog.spur/build.debug/mvm
index 235c119042..64279e784f 100755
--- a/building/linux64ARMv8/squeak.cog.spur/build.debug/mvm
+++ b/building/linux64ARMv8/squeak.cog.spur/build.debug/mvm
@@ -14,6 +14,7 @@ if [ `uname` = "OpenBSD" ]; then
     LIBRT=""
 # OpenBSD has problems with fast-bitblt under gcc and clang
     FASTBITBLT=""
+    OPT="$OPT -DMUSL"
 # Prefer clang over gcc if available
     if [ -n "$(command -v clang || true)" ]; then CC=clang; else CC=gcc; fi
 else # non-OpenBSD Linux
diff --git a/building/linux64ARMv8/squeak.cog.spur/build/mvm b/building/linux64ARMv8/squeak.cog.spur/build/mvm
index d299659380..5976ca0df6 100755
--- a/building/linux64ARMv8/squeak.cog.spur/build/mvm
+++ b/building/linux64ARMv8/squeak.cog.spur/build/mvm
@@ -6,7 +6,6 @@ INSTALLDIR=sqcogspur64ARMv8linuxht
 # tpr - add enablementisation of fast bitblt ben avison code
 MACHINE="-march=armv8-a -mtune=cortex-a72"
 OPT="-g -O2 -DNDEBUG -DDEBUGVM=0 -D_GNU_SOURCE -DUSEEVDEV"
-##OPT="-g -O3  -DMUSL -DNDEBUG -DDEBUGVM=0"
 
 if [ `uname` = "OpenBSD" ]; then
     DUALMAP="-DDUAL_MAPPED_CODE_ZONE=0"
@@ -16,6 +15,7 @@ if [ `uname` = "OpenBSD" ]; then
     LIBRT=""
 # OpenBSD has problems with fast-bitblt under gcc and clang
     FASTBITBLT=""
+    OPT="$OPT -DMUSL"
 # Prefer clang over gcc if available
     if [ -n "$(command -v clang || true)" ]; then CC=clang; else CC=gcc; fi
 else # non-OpenBSD Linux
diff --git a/building/linux64x64/squeak.cog.spur/build.debug/mvm b/building/linux64x64/squeak.cog.spur/build.debug/mvm
index 5814694860..9fadf6ea3f 100755
--- a/building/linux64x64/squeak.cog.spur/build.debug/mvm
+++ b/building/linux64x64/squeak.cog.spur/build.debug/mvm
@@ -21,6 +21,7 @@ if [ `uname` = "OpenBSD" ]; then
 	CFLAGS="$CFLAGS -I/usr/local/include"
 	LIBS="$LIBS -lexecinfo"
 	LDFLAGS="$LDFLAGS -L/usr/local/lib"
+	OPT="$OPT -DMUSL"
 fi
 
 if [ $# -ge 1 ]; then
diff --git a/building/linux64x64/squeak.cog.spur/build/mvm b/building/linux64x64/squeak.cog.spur/build/mvm
index 5f8639bf78..220d43b086 100755
--- a/building/linux64x64/squeak.cog.spur/build/mvm
+++ b/building/linux64x64/squeak.cog.spur/build/mvm
@@ -11,17 +11,17 @@ if [ -n "$(command -v clang || true)" ]; then CC=clang; else CC=gcc; fi
 # librt and libpthread funs now supplied by libc
 # Many Linux systems supply empty library files 
 # but OpenBSD does not.
-if [ `uname` = "OpenBSD" ]; then LIBRT=""; else LIBRT="-lrt"; fi
-
-CFLAGS="$OPT -msse2 -DCOGMTVM=0"
-LIBS=$LIBRT
-LDFLAGS=""
 
 # Special treatment for OpenBSD Linux
 if [ `uname` = "OpenBSD" ]; then
-	CFLAGS="$CFLAGS -I/usr/local/include"
+	OPT="$OPT -DMUSL"
+	CFLAGS="$CFLAGS $OPT -I/usr/local/include"
 	LIBS="$LIBS -lexecinfo"
 	LDFLAGS="$LDFLAGS -L/usr/local/lib"
+else
+	CFLAGS="$CFLAGS $OPT -msse2 -DCOGMTVM=0"
+	LIBS="$LIBS -lrt"
+	LDFLAGS="$LDFLAGS"
 fi
 
 if [ $# -ge 1 ]; then
diff --git a/platforms/unix/vm/sqUnixMemory.c b/platforms/unix/vm/sqUnixMemory.c
index 17d5343a26..681b0d800d 100644
--- a/platforms/unix/vm/sqUnixMemory.c
+++ b/platforms/unix/vm/sqUnixMemory.c
@@ -87,7 +87,11 @@ int mmapErrno = 0;
 #endif
 
 #define MAP_PROT	(PROT_READ | PROT_WRITE)
+#ifdef __OpenBSD__
+#define MAP_FLAGS	(MAP_ANON | MAP_PRIVATE | MAP_STACK)
+#else
 #define MAP_FLAGS	(MAP_ANON | MAP_PRIVATE)
+#endif
 
 extern int useMmap;
 /* Since Cog needs to make memory executable via mprotect, and since mprotect