Index: libntfs-3g/security.c
--- libntfs-3g/security.c.orig
+++ libntfs-3g/security.c
@@ -44,6 +44,10 @@
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
+#ifdef __OpenBSD__
+#include <sys/sysctl.h>
+#include <sys/types.h>
+#endif
 
 #include <unistd.h>
 #include <pwd.h>
@@ -1225,6 +1229,68 @@ static BOOL groupmember(struct SECURITY_CONTEXT *scx, 
 		close(fd);
 		}
 	}
+	return (ismember);
+}
+
+#elif defined(__OpenBSD__)
+
+static BOOL groupmember(struct SECURITY_CONTEXT *scx, uid_t uid, gid_t gid)
+{
+	struct kinfo_proc *kp;
+	size_t size;
+	int mib[6];
+	int ip, ig;
+	int pcnt;
+	gid_t *g;
+	pid_t tid;
+	BOOL ismember;
+
+	if (scx->vol->secure_flags & (1 << SECURITY_STATICGRPS))
+		ismember = staticgroupmember(scx, uid, gid);
+	else {
+		ismember = FALSE; /* default return */
+		tid = scx->tid;
+		mib[0] = CTL_KERN;
+		mib[1] = KERN_PROC;
+		mib[2] = KERN_PROC_ALL | KERN_PROC_SHOW_THREADS;
+		mib[3] = 0;
+		mib[4] = sizeof(struct kinfo_proc);
+		mib[5] = 0;
+		if (sysctl(mib, 6, NULL, &size, NULL, 0) == -1)
+			ntfs_log_error("Could not get size of process table: "
+			    "%s\n", strerror(errno));
+		else {
+			mib[5] = size / sizeof(struct kinfo_proc);
+			kp = malloc(size);
+			if ((kp == NULL) ||
+			    (sysctl(mib, 6, kp, &size, NULL, 0) == -1))
+				ntfs_log_error("Could not get process table: "
+				    "%s\n", strerror(errno));
+			else {
+				pcnt = size / sizeof(struct kinfo_proc);
+				ip = 0;
+				while ((kp[ip].p_tid != tid) && (ip < pcnt))
+					ip++;
+
+				if (ip < pcnt) {
+					if (kp[ip].p_gid == gid)
+						ismember = TRUE;
+					g = kp[ip].p_groups;
+					ig = 0;
+					while (!ismember
+					    && (ig < kp[ip].p_ngroups)
+					    && (*g != gid)) {
+						ig++;
+						g++;
+					}
+					if (ig < kp[ip].p_ngroups)
+						ismember = TRUE;
+				}
+				free(kp);
+			}
+		}
+	}
+
 	return (ismember);
 }