diff --git a/libguile/arrays.c b/libguile/arrays.c
index b4838e7e3..741cc564a 100644
--- a/libguile/arrays.c
+++ b/libguile/arrays.c
@@ -1126,7 +1126,8 @@ array_get_handle (SCM array, scm_t_array_handle *h)
   h->base = SCM_I_ARRAY_BASE (array);
 }
 
-SCM_ARRAY_IMPLEMENTATION (scm_i_tc16_array, 0xffff,
+SCM_ARRAY_IMPLEMENTATION (SCM_SMOB_TYPE_BITS (scm_i_tc16_array),
+                          SCM_SMOB_TYPE_MASK,
                           array_handle_ref, array_handle_set,
                           array_get_handle);
 
diff --git a/libguile/bitvectors.c b/libguile/bitvectors.c
index c3b6f3e4e..3e23adf8e 100644
--- a/libguile/bitvectors.c
+++ b/libguile/bitvectors.c
@@ -878,7 +878,8 @@ bitvector_get_handle (SCM bv, scm_t_array_handle *h)
   h->elements = h->writable_elements = BITVECTOR_BITS (bv);
 }
 
-SCM_ARRAY_IMPLEMENTATION (scm_tc16_bitvector, 0xffff,
+SCM_ARRAY_IMPLEMENTATION (SCM_SMOB_TYPE_BITS (scm_tc16_bitvector),
+                          SCM_SMOB_TYPE_MASK,
                           bitvector_handle_ref, bitvector_handle_set,
                           bitvector_get_handle);
 SCM_VECTOR_IMPLEMENTATION (SCM_ARRAY_ELEMENT_TYPE_BIT, scm_make_bitvector);
diff --git a/libguile/smob.h b/libguile/smob.h
index 06b1c48e1..f9b511066 100644
--- a/libguile/smob.h
+++ b/libguile/smob.h
@@ -161,6 +161,8 @@ while (0)
 #define SCM_SMOB_OBJECT_LOC(x)		(SCM_SMOB_OBJECT_1_LOC (x)))
 
 
+#define SCM_SMOB_TYPE_MASK		0xffff
+#define SCM_SMOB_TYPE_BITS(tc)		(tc)
 #define SCM_TC2SMOBNUM(x)		(0x0ff & ((x) >> 8))
 #define SCM_SMOBNUM(x)			(SCM_TC2SMOBNUM (SCM_CELL_TYPE (x)))
 /* SCM_SMOBNAME can be 0 if name is missing */
diff --git a/libguile/srfi-4.c b/libguile/srfi-4.c
index 3849776cd..45b9de066 100644
--- a/libguile/srfi-4.c
+++ b/libguile/srfi-4.c
@@ -883,7 +883,8 @@ uvec_get_handle (SCM v, scm_t_array_handle *h)
   h->elements = h->writable_elements = SCM_UVEC_BASE (v);
 }
 
-SCM_ARRAY_IMPLEMENTATION (scm_tc16_uvec, 0xffff,
+SCM_ARRAY_IMPLEMENTATION (SCM_SMOB_TYPE_BITS (scm_tc16_uvec),
+                          SCM_SMOB_TYPE_MASK,
                           uvec_handle_ref, uvec_handle_set,
                           uvec_get_handle);