diff --git a/build/Makefile b/build/Makefile
index 3ccab1c..a2d553f 100644
--- a/build/Makefile
+++ b/build/Makefile
@@ -9,7 +9,7 @@ MKFS=../tools/mkfs7
 A7OUT=../tools/a7out 
 FSCK=../tools/fsck7
 CCARGS=-Wno-multichar -Wno-implicit
-PDP7=pdp7
+PDP7?=pdp7
 
 # source dirs
 SYSSRC=../src/sys
diff --git a/build/os.mk b/build/os.mk
index 3e11dbb..af76036 100644
--- a/build/os.mk
+++ b/build/os.mk
@@ -9,6 +9,10 @@ ifeq ($(UNAME), Darwin)
 else 
 ifeq ($(UNAME), FreeBSD)
 	UNAME=FREEBSD
+else 
+ifeq ($(UNAME), OpenBSD)
+	UNAME=OPENBSD
+endif
 endif
 endif
 endif
@@ -23,6 +27,10 @@ ifeq ($(UNAME), FREEBSD)
 # FreeBSD
 	CC=cc
 	MAKE=gmake
+ifeq ($(UNAME), OPENBSD)
+# OpenBSD
+	CC=cc
+	MAKE=gmake
 else
 ifeq ($(UNAME), DARWIN)
 # Mac OS X
@@ -33,3 +41,4 @@ else
 endif
 endif
 endif
+endif