diff --git a/riscv_executor/src/lib.rs b/riscv_executor/src/lib.rs
index f15a46cb38..32b202708c 100644
--- a/riscv_executor/src/lib.rs
+++ b/riscv_executor/src/lib.rs
@@ -82,9 +82,9 @@ mod builder {
     pub struct TraceBuilder<'a, 'b> {
         trace: ExecutionTrace<'a>,
 
-        /// First register of current row.
-        /// Next row is reg_map.len() elems ahead.
-        curr_idx: usize,
+        /// First register of next row.
+        /// Curr row is reg_map.len() elems behind.
+        next_idx: usize,
 
         // index of special case registers to look after:
         x0_idx: usize,
@@ -112,7 +112,7 @@ mod builder {
             let values = vec![Elem::zero(); 2 * reg_map.len()];
 
             let mut ret = Self {
-                curr_idx: 0,
+                next_idx: reg_map.len(),
                 x0_idx: reg_map["x0"],
                 pc_idx: reg_map["pc"],
                 trace: ExecutionTrace { reg_map, values },
@@ -132,7 +132,8 @@ mod builder {
 
         /// get current value of register by register index instead of name
         fn g_idx(&self, idx: usize) -> Elem {
-            self.trace.values[self.curr_idx + idx]
+            let final_idx = self.next_idx - self.reg_len() + idx;
+            self.trace.values[final_idx]
         }
 
         /// set next value of register, accounting to x0 or pc writes
@@ -154,15 +155,14 @@ mod builder {
 
         /// raw set next value of register by register index instead of name
         fn s_idx(&mut self, idx: usize, value: Elem) {
-            let final_idx = self.curr_idx + self.reg_len() + idx;
-            self.trace.values[final_idx] = value;
+            self.trace.values[self.next_idx + idx] = value;
         }
 
         /// advance to next row, returns the index to the statement that must be
         /// executed now
         pub fn advance(&mut self) -> u32 {
-            self.curr_idx += self.reg_len();
-            self.trace.values.extend_from_within(self.curr_idx..);
+            self.trace.values.extend_from_within(self.next_idx..);
+            self.next_idx += self.reg_len();
 
             // advance the next statement
             let curr_line = self.next_statement_line;