diff --git a/src/flamenco/runtime/sysvar/fd_sysvar_slot_history.c b/src/flamenco/runtime/sysvar/fd_sysvar_slot_history.c
index c9ec548844..b73233ef6c 100644
--- a/src/flamenco/runtime/sysvar/fd_sysvar_slot_history.c
+++ b/src/flamenco/runtime/sysvar/fd_sysvar_slot_history.c
@@ -14,18 +14,19 @@ static const ulong slot_history_max_entries = 1024 * 1024;
 
 /* TODO: move into seperate bitvec library */
 static const ulong bits_per_block = 8 * sizeof(ulong);
-void fd_sysvar_slot_history_set( fd_slot_history_t* history, ulong i ) {
-  // Corrupt history, zero everything out
-  if ( i > history->next_slot && i - history->next_slot >= slot_history_max_entries ) {
-    for ( ulong j = 0; j < history->bits.bits->blocks_len; j++) {
-      history->bits.bits->blocks[ j ] = 0;
-    }
-  } else {
-    // Skipped slots, delete them from history
-    for (ulong j = history->next_slot; j < i; j++) {
-      ulong block_idx = (j / bits_per_block) % (history->bits.bits->blocks_len);
-      history->bits.bits->blocks[ block_idx ] &= ~( 1UL << ( j % bits_per_block ) );
-    }
+
+void
+fd_sysvar_slot_history_set( fd_slot_history_t * history,
+                            ulong               i ) {
+  if( FD_UNLIKELY( i > history->next_slot && i - history->next_slot >= slot_history_max_entries ) ) {
+    FD_LOG_WARNING(( "Ignoring out of bounds (i=%lu next_slot=%lu)", i, history->next_slot ));
+    return;
+  }
+
+  // Skipped slots, delete them from history
+  for( ulong j = history->next_slot; j < i; j++ ) {
+    ulong block_idx = (j / bits_per_block) % (history->bits.bits->blocks_len);
+    history->bits.bits->blocks[ block_idx ] &= ~( 1UL << ( j % bits_per_block ) );
   }
   ulong block_idx = (i / bits_per_block) % (history->bits.bits->blocks_len);
   history->bits.bits->blocks[ block_idx ] |= ( 1UL << ( i % bits_per_block ) );
@@ -50,10 +51,11 @@ int fd_sysvar_slot_history_write_history( fd_exec_slot_ctx_t * slot_ctx,
 }
 
 /* https://github.com/solana-labs/solana/blob/8f2c8b8388a495d2728909e30460aa40dcc5d733/sdk/program/src/slot_history.rs#L16 */
-void fd_sysvar_slot_history_init( fd_exec_slot_ctx_t * slot_ctx ) {
+void
+fd_sysvar_slot_history_init( fd_exec_slot_ctx_t * slot_ctx ) {
   /* Create a new slot history instance */
-  fd_slot_history_t history;
-  fd_slot_history_inner_t *inner = fd_valloc_malloc( slot_ctx->valloc, 8UL, sizeof(fd_slot_history_inner_t) );
+  fd_slot_history_t history = {0};
+  fd_slot_history_inner_t * inner = fd_valloc_malloc( slot_ctx->valloc, 8UL, sizeof(fd_slot_history_inner_t) );
   inner->blocks = fd_valloc_malloc( slot_ctx->valloc, 8UL, sizeof(ulong) * blocks_len );
   memset( inner->blocks, 0, sizeof(ulong) * blocks_len );
   inner->blocks_len = blocks_len;