diff --git a/Modules/_blake2/impl/blake2b-ref.c b/Modules/_blake2/impl/blake2b-ref.c
index 6b56fce3776..7c1301bef68 100644
--- a/Modules/_blake2/impl/blake2b-ref.c
+++ b/Modules/_blake2/impl/blake2b-ref.c
@@ -157,11 +157,12 @@ BLAKE2_LOCAL_INLINE(int) blake2b_init0( blake2b_state *S )
 int blake2b_init_param( blake2b_state *S, const blake2b_param *P )
 {
   const uint8_t *p = ( const uint8_t * )( P );
+  size_t i;
 
   blake2b_init0( S );
 
   /* IV XOR ParamBlock */
-  for( size_t i = 0; i < 8; ++i )
+  for( i = 0; i < 8; ++i )
     S->h[i] ^= load64( p + sizeof( S->h[i] ) * i );
 
   return 0;
@@ -392,14 +393,15 @@ int main( int argc, char **argv )
 {
   uint8_t key[BLAKE2B_KEYBYTES];
   uint8_t buf[KAT_LENGTH];
+  size_t i;
 
-  for( size_t i = 0; i < BLAKE2B_KEYBYTES; ++i )
+  for( i = 0; i < BLAKE2B_KEYBYTES; ++i )
     key[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
     buf[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
   {
     uint8_t hash[BLAKE2B_OUTBYTES];
     blake2b( hash, buf, key, BLAKE2B_OUTBYTES, i, BLAKE2B_KEYBYTES );
diff --git a/Modules/_blake2/impl/blake2b.c b/Modules/_blake2/impl/blake2b.c
index 784ec00434e..58c79fa8489 100644
--- a/Modules/_blake2/impl/blake2b.c
+++ b/Modules/_blake2/impl/blake2b.c
@@ -426,14 +426,15 @@ int main( int argc, char **argv )
 {
   uint8_t key[BLAKE2B_KEYBYTES];
   uint8_t buf[KAT_LENGTH];
+  size_t i;
 
-  for( size_t i = 0; i < BLAKE2B_KEYBYTES; ++i )
+  for( i = 0; i < BLAKE2B_KEYBYTES; ++i )
     key[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
     buf[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
   {
     uint8_t hash[BLAKE2B_OUTBYTES];
     blake2b( hash, buf, key, BLAKE2B_OUTBYTES, i, BLAKE2B_KEYBYTES );
diff --git a/Modules/_blake2/impl/blake2s-ref.c b/Modules/_blake2/impl/blake2s-ref.c
index 0cf4707da12..157e9a2298a 100644
--- a/Modules/_blake2/impl/blake2s-ref.c
+++ b/Modules/_blake2/impl/blake2s-ref.c
@@ -154,7 +154,7 @@ int blake2s_init_param( blake2s_state *S, const blake2s_param *P )
   blake2s_init0( S );
 
   /* IV XOR ParamBlock */
-  for( size_t i = 0; i < 8; ++i )
+  for( i = 0; i < 8; ++i )
     S->h[i] ^= load32( &p[i] );
 
   return 0;
@@ -219,11 +219,12 @@ static int blake2s_compress( blake2s_state *S, const uint8_t block[BLAKE2S_BLOCK
 {
   uint32_t m[16];
   uint32_t v[16];
+  size_t i;
 
-  for( size_t i = 0; i < 16; ++i )
+  for( i = 0; i < 16; ++i )
     m[i] = load32( block + i * sizeof( m[i] ) );
 
-  for( size_t i = 0; i < 8; ++i )
+  for( i = 0; i < 8; ++i )
     v[i] = S->h[i];
 
   v[ 8] = blake2s_IV[0];
@@ -267,7 +268,7 @@ static int blake2s_compress( blake2s_state *S, const uint8_t block[BLAKE2S_BLOCK
   ROUND( 8 );
   ROUND( 9 );
 
-  for( size_t i = 0; i < 8; ++i )
+  for( i = 0; i < 8; ++i )
     S->h[i] = S->h[i] ^ v[i] ^ v[i + 8];
 
 #undef G
@@ -381,14 +382,15 @@ int main( int argc, char **argv )
 {
   uint8_t key[BLAKE2S_KEYBYTES];
   uint8_t buf[KAT_LENGTH];
+  size_t i;
 
-  for( size_t i = 0; i < BLAKE2S_KEYBYTES; ++i )
+  for( i = 0; i < BLAKE2S_KEYBYTES; ++i )
     key[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
     buf[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
   {
     uint8_t hash[BLAKE2S_OUTBYTES];
     blake2s( hash, buf, key, BLAKE2S_OUTBYTES, i, BLAKE2S_KEYBYTES );
diff --git a/Modules/_blake2/impl/blake2s.c b/Modules/_blake2/impl/blake2s.c
index 3aea4af3035..ccad66266bb 100644
--- a/Modules/_blake2/impl/blake2s.c
+++ b/Modules/_blake2/impl/blake2s.c
@@ -407,14 +407,15 @@ int main( int argc, char **argv )
 {
   uint8_t key[BLAKE2S_KEYBYTES];
   uint8_t buf[KAT_LENGTH];
+  size_t i;
 
-  for( size_t i = 0; i < BLAKE2S_KEYBYTES; ++i )
+  for( i = 0; i < BLAKE2S_KEYBYTES; ++i )
     key[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
     buf[i] = ( uint8_t )i;
 
-  for( size_t i = 0; i < KAT_LENGTH; ++i )
+  for( i = 0; i < KAT_LENGTH; ++i )
   {
     uint8_t hash[BLAKE2S_OUTBYTES];