diff --git a/include/sprs.h b/include/sprs.h
index f7960b2..12abc27 100644
--- a/include/sprs.h
+++ b/include/sprs.h
@@ -33,7 +33,7 @@ struct sprs_element_s {
   /**
    * The index of this element in the dense array.
    */
-  int index;
+  size_t index;
   /**
    * A piece of data (optional) associated with this index.
    */
@@ -47,11 +47,11 @@ struct sprs_s {
   /**
    * The maximum size of the set. This is the limit for integer indices.
    */
-  int capacity;
+  size_t capacity;
   /**
    * The current size of the sparse set, and the next available index in the dense array.
    */
-  int size;
+  size_t size;
 
   /**
    * The dense array.
@@ -80,7 +80,7 @@ void sprs_init(sprs* sprs);
  * @param size the maximum capacity of the sparse set to use.
  * @return LIBDS_SUCCESS if all goes well, or LIBDS_MALLOC if an allocation failed.
  */
-libds_result sprs_setup(sprs* sprs, int size);
+libds_result sprs_setup(sprs* sprs, size_t size);
 /**
  * Frees memory allocated by the sparse set, and resets its capacity and size.
  * @param sprs the sparse set to free.
diff --git a/src/sprs.c b/src/sprs.c
index ef1271a..e3efca1 100644
--- a/src/sprs.c
+++ b/src/sprs.c
@@ -7,7 +7,7 @@ void sprs_init(sprs* sprs){
   sprs->dense = NULL;
   sprs->sparse = NULL;
 }
-libds_result sprs_setup(sprs* sprs, int size){
+libds_result sprs_setup(sprs* sprs, size_t size){
   libds_result result = LIBDS_SUCCESS;
   sprs->sparse = malloc(sizeof(*(sprs->sparse)) * size);
   sprs->dense = malloc(sizeof(*(sprs->dense)) * size);