diff --git a/terminatorlib/freebsd.py b/terminatorlib/freebsd.py
index 221d5146..8937dc4d 100644
--- a/terminatorlib/freebsd.py
+++ b/terminatorlib/freebsd.py
@@ -39,20 +39,19 @@ class kinfo_file(Structure):
       ('kf_sa_peer',       sockaddr_storage),
   ]
 
+libc = CDLL('libc.so')
+
+len = c_uint(sizeof(c_uint))
+ver = c_uint(0)
+
+if (libc.sysctlbyname('kern.osreldate', byref(ver), byref(len), None, 0) < 0):
+  raise OSError, "sysctlbyname returned < 0"
+
+# kern.proc.filedesc added for procstat(1) after these __FreeBSD_versions
+if ver.value < 700104 and ver.value < 800019:
+  raise NotImplementedError, "cwd detection requires a recent 7.0-STABLE or 8-CURRENT"
 
 def get_process_cwd(pid):
-  libc = CDLL('libc.so')
-
-  len = c_uint(sizeof(c_uint))
-  ver = c_uint(0)
-
-  if (libc.sysctlbyname('kern.osreldate', byref(ver), byref(len), None, 0) < 0):
-    return None
-
-  # kern.proc.filedesc added for procstat(1) after these __FreeBSD_versions
-  if ver.value < 700104 and ver.value < 800019:
-    return None
-
   # /usr/include/sys/sysctl.h
   # CTL_KERN, KERN_PROC, KERN_PROC_FILEDESC
   oid = (c_uint * 4)(1, 14, 14, pid)