diff --git a/include/ucore/bitvec.h b/include/ucore/bitvec.h
index 5eec670..06085b8 100644
--- a/include/ucore/bitvec.h
+++ b/include/ucore/bitvec.h
@@ -1,13 +1,18 @@
 #ifndef UC_BITEVEC_H_
 #define UC_BITEVEC_H_
 
+#include <limits.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/** Backing type of the bit vector*/
+typedef unsigned long uc_bv_integer;
+
 struct UCBitVec {
     //storage for the bits
-    unsigned long *vec;
+    uc_bv_integer *vec;
     //length in bytes of the above vec.
     size_t vec_len;
 };
@@ -15,11 +20,11 @@ struct UCBitVec {
 /**
  *  Evaluates the length required for a bitvec to store nbit bits.
  */
-#define UC_BV_LEN(nbits)   ((nbits/(sizeof(unsigned long)*CHAR_BIT)) + (nbits % (sizeof(unsigned long)*CHAR_BIT) == 0 ? 0 : 1))
+#define UC_BV_LEN(nbits)   ((nbits/(sizeof(uc_bv_integer)*CHAR_BIT)) + (nbits % (sizeof(uc_bv_integer)*CHAR_BIT) == 0 ? 0 : 1))
 
 /**
  * Use as :
- * unsigned long v[10];
+ * uc_bv_integer v[10];
  * struct UCBitVec v = BITVEC_STATIC_INIT(v);
  */
 #define UC_BV_STATIC_INIT(vec_data)\
diff --git a/src/bitvec.c b/src/bitvec.c
index abab68b..edb6cc3 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -1,7 +1,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
-#include <limits.h>
 #include "ucore/bitvec.h"
 
 #ifdef __GNUC__
@@ -14,12 +13,12 @@
 
 static inline int bit_index(int b)
 {
-     return b / (sizeof(unsigned long) * CHAR_BIT);
+     return b / (sizeof(uc_bv_integer) * CHAR_BIT);
 }
 
 static inline int bit_offset(int b)
 { 
-    return b % (sizeof(unsigned long) * CHAR_BIT);
+    return b % (sizeof(uc_bv_integer) * CHAR_BIT);
 }
 
 struct UCBitVec *uc_bv_new(size_t nbits)
@@ -29,7 +28,7 @@ struct UCBitVec *uc_bv_new(size_t nbits)
     if (v == NULL)
         return NULL;
     v->vec_len = UC_BV_LEN(nbits);
-    v->vec = malloc(v->vec_len * sizeof(unsigned long));
+    v->vec = malloc(v->vec_len * sizeof(uc_bv_integer));
     if (v->vec == NULL) {
         free(v);
         return NULL;
@@ -81,11 +80,11 @@ void uc_bv_set_bits_from_array(struct UCBitVec *v,char *array,size_t array_len)
 
 void uc_bv_clr_all(struct UCBitVec *v)
 {
-    memset(v->vec,0, v->vec_len * sizeof(unsigned long));
+    memset(v->vec,0, v->vec_len * sizeof(uc_bv_integer));
 }
 
 void uc_bv_set_all(struct UCBitVec *v)
 {
-    memset(v->vec,0xff,v->vec_len * sizeof(unsigned long));
+    memset(v->vec,0xff,v->vec_len * sizeof(uc_bv_integer));
 }
 
diff --git a/test/test_bitvec.c b/test/test_bitvec.c
index 3805ebb..d1a0a6b 100644
--- a/test/test_bitvec.c
+++ b/test/test_bitvec.c
@@ -3,7 +3,7 @@
 
 
 START_TEST (test_bitvec_1)
-    unsigned long s[3] = {0};
+    uc_bv_integer s[3] = {0};
     struct UCBitVec v = UC_BV_STATIC_INIT(s);
     size_t i;
 
@@ -12,7 +12,7 @@ START_TEST (test_bitvec_1)
 END_TEST
 
 START_TEST (test_bitvec_2)
-    unsigned long s[3] = {0};
+    uc_bv_integer s[3] = {0};
     struct UCBitVec v = UC_BV_STATIC_INIT(s);
     size_t i;
 
@@ -24,17 +24,17 @@ START_TEST (test_bitvec_2)
 END_TEST
 
 START_TEST (test_bitvec_clearbit)
-    unsigned long s[3] = {-1, -1, -1};
+    uc_bv_integer s[3] = {-1, -1, -1};
     struct UCBitVec v = UC_BV_STATIC_INIT(s);
     size_t i;
 
-    for (i = 0; i < sizeof(unsigned long)  * 8; i++)
+    for (i = 0; i < sizeof(uc_bv_integer)  * 8; i++)
         fail_if(uc_bv_get_bit(&v, i) != 1 , "bit %zu is not 1", i);
 
-    for (i = 0; i < sizeof(unsigned long) * 8; i++)
+    for (i = 0; i < sizeof(uc_bv_integer) * 8; i++)
         uc_bv_clr_bit(&v, i);
 
-    for (i = 0; i < sizeof(unsigned long)  * 8; i++)
+    for (i = 0; i < sizeof(uc_bv_integer)  * 8; i++)
         fail_if(uc_bv_get_bit(&v, i) != 0 , "bit %zu is not 0", i);
 
 END_TEST
@@ -63,7 +63,7 @@ START_TEST (test_bitvec_setall_clearall)
 
     uc_bv_clr_all(v);
 
-    for (i = 0; i < sizeof(unsigned long)  * 8; i++)
+    for (i = 0; i < sizeof(uc_bv_integer)  * 8; i++)
         fail_if(uc_bv_get_bit(v, i) != 0 , "bit %zu is not 0", i);
 
     uc_bv_free(v);