diff --git a/include/ht.h b/include/ht.h
index 4f3586a..73b669b 100644
--- a/include/ht.h
+++ b/include/ht.h
@@ -45,21 +45,21 @@ struct ht_s {
    * @param input the data being hashed.
    * @return the data's hash.
    */
-  unsigned long (*hash_func)(void* input);
+  unsigned long (*hash_func)(const void* input);
   /**
    * Function to compare two keys.
    * @param given_key the key being used to retrieve data
    * @param current_key the key of a hash table node
    * @return nonzero value if the keys match.
    */
-  int (*cmp_func)(void* given_key, void* current_key);
+  int (*cmp_func)(const void* given_key, const void* current_key);
   /**
    * Function used to duplicate the given key and
    * store it in a node.
    * @param key the key to copy
    * @return pointer to a new key.
    */
-  void* (*copy_func)(void* key);
+  void* (*copy_func)(const void* key);
   /**
    * Function used to free a previously copied key.
    * @param key the key to free.
@@ -76,7 +76,7 @@ typedef struct ht_s ht;
  * @param key the data to hash.
  * @return the produced hashed integer.
  */
-unsigned long ht_default_hash_func(void* key);
+unsigned long ht_default_hash_func(const void* key);
 /**
  * The default key comparison function.
  * Assumes both keys are strings and uses strcmp.
@@ -84,13 +84,13 @@ unsigned long ht_default_hash_func(void* key);
  * @param b the key compared against
  * @return true if the keys represent the same string.
  */
-int ht_default_cmp_func(void* a, void* b);
+int ht_default_cmp_func(const void* a, const void* b);
 /**
  * The default key copy function.
  * @param key the key being copied
  * @return a pointer to the copy of the key.
  */
-void* ht_default_copy_func(void* key);
+void* ht_default_copy_func(const void* key);
 /**
  * The default key free function. Simply calls free()
  * @param key the key to free.
@@ -117,20 +117,20 @@ void ht_free(ht* ht);
  * @param value the value to store.
  * @return LIBDS_SUCCESS if all goes well, LIBDS_MALLOC if an allocation fails.
  */
-libds_result ht_put(ht* ht, void* key, void* value);
+libds_result ht_put(ht* ht, const void* key, void* value);
 /**
  * Retrieves a value from the hash table.
  * @param ht the hash table to retrieve a value from.
  * @param key the key to use to find the data.
  * @return the data, or NULL if it is not found.
  */
-void* ht_get(ht* ht, void* key);
+void* ht_get(ht* ht, const void* key);
 /**
  * Removes a value from the hash table.
  * @param ht the hash table to remove a value from.
  * @param key the key to use to find the data.
  */
-void ht_remove(ht* ht, void* key);
+void ht_remove(ht* ht, const void* key);
 
 /**
  * Runs through every element in the hash table, and compares it against the
diff --git a/include/libds.h b/include/libds.h
index 0c9b566..d951a7b 100644
--- a/include/libds.h
+++ b/include/libds.h
@@ -15,7 +15,7 @@ typedef enum libds_result_e libds_result;
  * The function should take two elements, and, if they match, return 1. Otherwise, it should
  * return 0.
  */
-typedef int (*compare_func)(void*, void*);
+typedef int (*compare_func)(const void*, const void*);
 /**
  * Foreach function type.
  * Foreach functions are passed to _foreach calls.
@@ -29,13 +29,13 @@ typedef int (*foreach_func)(void*, va_list);
  * @param b The second piece of data being compared
  * @return always true, i.e 1
  */
-int compare_always(void* a, void* b);
+int compare_always(const void* a, const void* b);
 /**
  * A compare_func implementation that compares two pointers using ==.
  * @param a the first piece of data being compared
  * @param b the second piece of data being compared
  * @return true if a and b are the same value.
  */
-int compare_pointer(void* a, void* b);
+int compare_pointer(const void* a, const void* b);
 
 #endif
diff --git a/src/ht.c b/src/ht.c
index 7a3c48e..ba3d6e9 100644
--- a/src/ht.c
+++ b/src/ht.c
@@ -2,11 +2,11 @@
 #include <stdlib.h>
 #include <string.h>
 
-unsigned long ht_default_hash_func(void* data) {
+unsigned long ht_default_hash_func(const void* data) {
   const unsigned long fnv_prime = 16777619;
   const unsigned long fnv_offset_basis = 2166136261;
   unsigned long hash;
-  char* string;
+  const char* string;
   hash = fnv_offset_basis;
   string = data;
   while (*string) {
@@ -15,8 +15,8 @@ unsigned long ht_default_hash_func(void* data) {
   }
   return hash;
 }
-int ht_default_cmp_func(void* a, void* b) { return strcmp(a, b) == 0; }
-void* ht_default_copy_func(void* from) {
+int ht_default_cmp_func(const void* a, const void* b) { return strcmp(a, b) == 0; }
+void* ht_default_copy_func(const void* from) {
   void* copy = malloc(sizeof(char) * (strlen(from) + 1));
   if (copy) {
     strcpy(copy, from);
@@ -48,7 +48,7 @@ void ht_free(ht* ht) {
   ht->hash_func = NULL;
 }
 
-libds_result ht_put(ht* ht, void* key, void* data) {
+libds_result ht_put(ht* ht, const void* key, void* data) {
   libds_result result = LIBDS_SUCCESS;
   ht_node* new_node = NULL;
   void* new_key = NULL;
@@ -69,7 +69,7 @@ libds_result ht_put(ht* ht, void* key, void* data) {
 
   return result;
 }
-void* ht_get(ht* ht, void* key) {
+void* ht_get(ht* ht, const void* key) {
   void* data = NULL;
   ht_node* search_node;
   unsigned long key_int = ht->hash_func(key) % LIBDS_HT_SIZE;
@@ -84,7 +84,7 @@ void* ht_get(ht* ht, void* key) {
 
   return data;
 }
-void ht_remove(ht* ht, void* key) {
+void ht_remove(ht* ht, const void* key) {
   ht_node** search_ptr;
   unsigned long key_int = ht->hash_func(key) % LIBDS_HT_SIZE;
 
diff --git a/src/libds.c b/src/libds.c
index 6b07d43..24843ca 100644
--- a/src/libds.c
+++ b/src/libds.c
@@ -1,4 +1,4 @@
 #include "libds.h"
 
-int compare_always(void* a, void* b) { return 1; }
-int compare_pointer(void* a, void* b) { return a == b; }
+int compare_always(const void* a, const void* b) { return 1; }
+int compare_pointer(const void* a, const void* b) { return a == b; }
diff --git a/src/main.c b/src/main.c
index 2caf821..9b4da95 100644
--- a/src/main.c
+++ b/src/main.c
@@ -14,7 +14,7 @@ int _test_vec_foreach_func(void* data, va_list args) {
   *sum += *real_data;
   return 0;
 }
-int _test_vec_find_string(void* a, void* b) { return strcmp(a, b) == 0; }
+int _test_vec_find_string(const void* a, const void* b) { return strcmp(a, b) == 0; }
 
 int test_vec_basic() {
   vec test_vec;