diff --git a/include/sprs.h b/include/sprs.h
index 59582b0..c7b1714 100644
--- a/include/sprs.h
+++ b/include/sprs.h
@@ -58,7 +58,7 @@ struct sprs_s {
    * The dense array.
    * This is a pointer so that an array of a certain size can be allocated as needed.
    */
-  int* dense;
+  size_t* dense;
   /**
    * The sparse array.
    * This is a pointer so that an array of a certain size can be allocated as needed.
@@ -94,14 +94,14 @@ void sprs_free(sprs* sprs);
  * @param index the index at which to store the value
  * @param data the value to store.
  */
-void sprs_put(sprs* sprs, int index, void* data);
+void sprs_put(sprs* sprs, size_t index, void* data);
 /**
  * Checks if the sparse set contains data under a given index.
  * @param sprs the sparse set to check.
  * @param index the index for which to check.
  * @return 1 if the index exists, 0 if not.
  */
-int sprs_contains(sprs* sprs, int index);
+int sprs_contains(sprs* sprs, size_t index);
 /**
  * Gets the value stored under the given sparse set index.
  * This will check for whether the index is in the sparse set first,
@@ -113,7 +113,7 @@ int sprs_contains(sprs* sprs, int index);
  * @param index the index from under which to retrieve the value.
  * @return the value stored under the index, or NULL if there is nothing there.
  */
-void* sprs_get(sprs* sprs, int index);
+void* sprs_get(sprs* sprs, size_t index);
 
 /**
  * Runs through every element in the sparse set, and compares it against the
diff --git a/src/sprs.c b/src/sprs.c
index 305e01a..99009c6 100644
--- a/src/sprs.c
+++ b/src/sprs.c
@@ -30,17 +30,17 @@ void sprs_free(sprs* sprs){
   sprs->dense = NULL;
   sprs->sparse = NULL;
 }
-void sprs_put(sprs* sprs, int index, void* data){
+void sprs_put(sprs* sprs, size_t index, void* data){
   if(index < sprs->capacity && sprs->size < sprs->capacity){
     sprs->dense[sprs->size++] = index;
     sprs->sparse[index].index = sprs->size - 1;
     sprs->sparse[index].data = data;
   }
 }
-int sprs_contains(sprs* sprs, int index){
-  return index >= 0 && sprs->sparse[index].index < sprs->size && sprs->dense[sprs->sparse[index].index] == index;
+int sprs_contains(sprs* sprs, size_t index){
+  return sprs->sparse[index].index < sprs->size && sprs->dense[sprs->sparse[index].index] == index;
 }
-void* sprs_get(sprs* sprs, int index){
+void* sprs_get(sprs* sprs, size_t index){
   void* data = NULL;
   if(sprs_contains(sprs, index)){
     data = sprs->sparse[index].data;