diff --git a/lib/keccak/keccak.c b/lib/keccak/keccak.c
index 8f51c1af..a621e665 100644
--- a/lib/keccak/keccak.c
+++ b/lib/keccak/keccak.c
@@ -8,6 +8,7 @@
 #if !__has_builtin(__builtin_memcpy) && !defined(__GNUC__)
 #include <string.h>
 #define __builtin_memcpy memcpy
+#define __builtin_memset memset
 #endif
 
 #if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -399,10 +400,10 @@ static inline ALWAYS_INLINE void keccak_update(
     size_t i;
 
     size_t block_size_b = ctx->block_size / word_size;  // block size in bytes
-    size_t last_word_unfilled_size =  // calculate unfilled space in last word, ignore if all empty
-        (word_size - (size_t)(ctx->last_word_iter - (uint8_t*)&(ctx->last_word))) % word_size;
-    size_t state_unfilled_size =  // calculate unfilled space in state, ignore if all empty
-        (block_size_b - (size_t)(ctx->state_iter - ctx->state)) % block_size_b;
+    size_t last_word_unfilled_size =  // calculate unfilled space in last word
+        (word_size - (size_t)(ctx->last_word_iter - (uint8_t*)&(ctx->last_word)));
+    size_t state_unfilled_size =  // calculate unfilled space in state
+        (block_size_b - (size_t)(ctx->state_iter - ctx->state));
 
     // fill the last word unfilled space with bytes until it's full
     while(last_word_unfilled_size > 0 && size > 0)
diff --git a/test/unittests/test_keccak.cpp b/test/unittests/test_keccak.cpp
index 8960ce0e..3a1ffff6 100644
--- a/test/unittests/test_keccak.cpp
+++ b/test/unittests/test_keccak.cpp
@@ -8,6 +8,8 @@
 
 #include <gtest/gtest.h>
 
+#include <random>
+
 using namespace ethash;
 
 struct keccak_test_case
@@ -292,7 +294,7 @@ TEST(keccak, iuf_test_simple)
         const auto h256 = keccak256(data, t.input_size);
         ASSERT_EQ(to_hex(h256), t.expected_hash256) << t.input_size;
 
-        struct ethash_keccak256_context ctx;
+        struct ethash_keccak256_context ctx = {};
         keccak256_init(&ctx);
         keccak256_update(&ctx, data, t.input_size);
         const auto h2561 = keccak256_final(&ctx);
@@ -328,7 +330,7 @@ TEST(keccak, iuf_test_simple)
         i = 0;
         while(i <  t.input_size) 
         {
-            step = (size_t)rand() % 300;
+            step = (size_t)arc4random() % 300;
             size_t l = t.input_size - i >= step ? step : t.input_size - i;
             keccak256_update(&ctx, &data[i], l);
             i = i + step;
@@ -345,7 +347,7 @@ TEST(keccak, iuf_test_simple_2)
     for (auto& t : test_cases)
     {
         {
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             keccak256_update_2(&ctx, data, t.input_size);
             const auto h256 = keccak256_final_2(&ctx);
@@ -355,7 +357,7 @@ TEST(keccak, iuf_test_simple_2)
         {
             size_t i;
 
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             for(i = 0; i <  t.input_size; ++i) 
             {
@@ -368,7 +370,7 @@ TEST(keccak, iuf_test_simple_2)
         {
             size_t i;
             size_t step = 0;
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             for(step = 1; step < 256; ++step) 
             {
                 keccak256_init_2(&ctx);
@@ -384,14 +386,14 @@ TEST(keccak, iuf_test_simple_2)
         }
 
         {
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             
             size_t i = 0;
             size_t step = 0;
             while(i <  t.input_size) 
             {
-                step = (size_t)rand() % 300;
+                step = (size_t)arc4random() % 300;
                 size_t l = t.input_size - i >= step ? step : t.input_size - i;
                 keccak256_update_2(&ctx, &data[i], l);
                 i = i + step;
@@ -400,4 +402,4 @@ TEST(keccak, iuf_test_simple_2)
             ASSERT_EQ(to_hex(h256), t.expected_hash256) << t.input_size;
         }
     }
-}
\ No newline at end of file
+}