diff --git a/sys/kern/kern_osd.c b/sys/kern/kern_osd.c
--- a/sys/kern/kern_osd.c
+++ b/sys/kern/kern_osd.c
@@ -73,6 +73,9 @@
 	}								\
 } while (0)
 
+#define	OSD_METHOD(osdm, slot, method)	\
+    ((osdm).osd_methods[((slot) - 1) * (osdm).osd_nmethods + (method)])
+
 static void do_osd_del(u_int type, struct osd *osd, u_int slot,
     int list_locked);
 
@@ -139,8 +142,8 @@
 	osdm[type].osd_destructors[i] = destructor;
 	if (osdm[type].osd_nmethods != 0) {
 		for (m = 0; m < osdm[type].osd_nmethods; m++)
-			osdm[type].osd_methods[i * osdm[type].osd_nmethods + m]
-			    = methods != NULL ? methods[m] : NULL;
+			OSD_METHOD(osdm[type], i + 1, m) =
+			    methods != NULL ? methods[m] : NULL;
 	}
 	sx_xunlock(&osdm[type].osd_module_lock);
 	return (i + 1);
@@ -391,8 +394,7 @@
 		/* Hole in the slot map; avoid dereferencing. */
 		if (osdm[type].osd_destructors[i] == NULL)
 			continue;
-		methodfun = osdm[type].osd_methods[i * osdm[type].osd_nmethods +
-		    method];
+		methodfun = OSD_METHOD(osdm[type], i + 1, method);
 		if (methodfun != NULL && (error = methodfun(obj, data)) != 0)
 			break;
 	}