diff --git a/src/libethash/data_sizes.h b/src/libethash/data_sizes.h
index 3b747b3e..cf52ae4f 100644
--- a/src/libethash/data_sizes.h
+++ b/src/libethash/data_sizes.h
@@ -48,7 +48,7 @@ extern "C" {
 //             Sow[i*HashBytes]; j++]]]][[2]][[1]]
 
 
-static const size_t dag_sizes[2048] = {
+static const uint64_t dag_sizes[2048] = {
         1073739904U, 1082130304U, 1090514816U, 1098906752U, 1107293056U,
         1115684224U, 1124070016U, 1132461952U, 1140849536U, 1149232768U,
         1157627776U, 1166013824U, 1174404736U, 1182786944U, 1191180416U,
@@ -477,7 +477,7 @@ static const size_t dag_sizes[2048] = {
 //         While[! PrimeQ[i], i--];
 //         Sow[i*HashBytes]; j++]]]][[2]][[1]]
 
-const size_t cache_sizes[2048] = {
+const uint64_t cache_sizes[2048] = {
         16776896U, 16907456U, 17039296U, 17170112U, 17301056U, 17432512U, 17563072U,
         17693888U, 17824192U, 17955904U, 18087488U, 18218176U, 18349504U, 18481088U,
         18611392U, 18742336U, 18874304U, 19004224U, 19135936U, 19267264U, 19398208U,
diff --git a/src/libethash/ethash.h b/src/libethash/ethash.h
index 809b7cce..cc3d634d 100644
--- a/src/libethash/ethash.h
+++ b/src/libethash/ethash.h
@@ -43,8 +43,8 @@ extern "C" {
 #endif
 
 typedef struct ethash_params {
-    size_t full_size;               // Size of full data set (in bytes, multiple of mix size (128)).
-    size_t cache_size;              // Size of compute cache (in bytes, multiple of node size (64)).
+    uint64_t full_size;               // Size of full data set (in bytes, multiple of mix size (128)).
+    uint64_t cache_size;              // Size of compute cache (in bytes, multiple of node size (64)).
 } ethash_params;
 
 typedef struct ethash_return_value {
@@ -52,8 +52,8 @@ typedef struct ethash_return_value {
     uint8_t mix_hash[32];
 } ethash_return_value;
 
-size_t ethash_get_datasize(const uint32_t block_number);
-size_t ethash_get_cachesize(const uint32_t block_number);
+uint64_t ethash_get_datasize(const uint32_t block_number);
+uint64_t ethash_get_cachesize(const uint32_t block_number);
 
 // Initialize the Parameters
 static inline int ethash_params_init(ethash_params *params, const uint32_t block_number) {
diff --git a/src/libethash/internal.c b/src/libethash/internal.c
index 9b6629f7..ea0b630f 100644
--- a/src/libethash/internal.c
+++ b/src/libethash/internal.c
@@ -36,13 +36,13 @@
 #include "sha3.h"
 #endif // WITH_CRYPTOPP
 
-size_t ethash_get_datasize(const uint32_t block_number) {
+uint64_t ethash_get_datasize(const uint32_t block_number) {
     if (block_number / EPOCH_LENGTH >= 2048)
         return 0;
     return dag_sizes[block_number / EPOCH_LENGTH];
 }
 
-size_t ethash_get_cachesize(const uint32_t block_number) {
+uint64_t ethash_get_cachesize(const uint32_t block_number) {
     if (block_number / EPOCH_LENGTH >= 2048)
         return 0;
     return cache_sizes[block_number / EPOCH_LENGTH];
diff --git a/src/python/core.c b/src/python/core.c
index 35973599..6d0a40ad 100644
--- a/src/python/core.c
+++ b/src/python/core.c
@@ -58,7 +58,7 @@ mkcache_bytes(PyObject *self, PyObject *args) {
     }
 
     ethash_params params;
-    params.cache_size = (size_t) cache_size;
+    params.cache_size = (uint64_t) cache_size;
     ethash_cache cache;
     cache.mem = malloc(cache_size);
     ethash_mkcache(&cache, &params, (uint8_t *) seed);
@@ -92,8 +92,8 @@ calc_dataset_bytes(PyObject *self, PyObject *args) {
     }
 
     ethash_params params;
-    params.cache_size = (size_t) cache_size;
-    params.full_size = (size_t) full_size;
+    params.cache_size = (uint64_t) cache_size;
+    params.full_size = (uint64_t) full_size;
     ethash_cache cache;
     cache.mem = (void *) cache_bytes;
     void *mem = malloc(params.full_size);
@@ -138,8 +138,8 @@ hashimoto_light(PyObject *self, PyObject *args) {
 
     ethash_return_value out;
     ethash_params params;
-    params.cache_size = (size_t) cache_size;
-    params.full_size = (size_t) full_size;
+    params.cache_size = (uint64_t) cache_size;
+    params.full_size = (uint64_t) full_size;
     ethash_cache cache;
     cache.mem = (void *) cache_bytes;
     ethash_light(&out, &cache, &params, (uint8_t *) header, nonce);
@@ -175,7 +175,7 @@ hashimoto_full(PyObject *self, PyObject *args) {
 
     ethash_return_value out;
     ethash_params params;
-    params.full_size = (size_t) full_size;
+    params.full_size = (uint64_t) full_size;
     ethash_full(&out, (void *) full_bytes, &params, (uint8_t *) header, nonce);
     return Py_BuildValue("{s:s#, s:s#}",
             "mix digest", out.mix_hash, 32,
@@ -216,7 +216,7 @@ mine(PyObject *self, PyObject *args) {
 
     ethash_return_value out;
     ethash_params params;
-    params.full_size = (size_t) full_size;
+    params.full_size = (uint64_t) full_size;
 
     // TODO: Multi threading?
     do {
diff --git a/test/c/test.cpp b/test/c/test.cpp
index 9c0213d9..8c854ecb 100644
--- a/test/c/test.cpp
+++ b/test/c/test.cpp
@@ -17,7 +17,7 @@
 #include <boost/test/unit_test.hpp>
 #include <iostream>
 
-std::string bytesToHexString(const uint8_t *str, const size_t s) {
+std::string bytesToHexString(const uint8_t *str, const uint32_t s) {
     std::ostringstream ret;
 
     for (int i = 0; i < s; ++i)