diff --git a/cpu/src/lib.rs b/cpu/src/lib.rs
index 509471a..01a4670 100644
--- a/cpu/src/lib.rs
+++ b/cpu/src/lib.rs
@@ -11,7 +11,7 @@ use core::marker::Sync;
 use core::mem::transmute;
 use valida_bus::{MachineWithGeneralBus, MachineWithMemBus, MachineWithProgramBus};
 use valida_machine::{
-    index_of_word, index_to_word, instructions, AdviceProvider, Chip, Instruction, InstructionWord,
+    index_of_byte, index_to_word, instructions, AdviceProvider, Chip, Instruction, InstructionWord,
     Interaction, Operands, Word,
 };
 use valida_memory::{MachineWithMemoryChip, Operation as MemoryOperation};
@@ -495,16 +495,16 @@ where
         );
 
         // The array index of the word for the byte to read from
-        let index_of_read = index_of_word(read_addr.into());
+        let index_of_read = index_of_byte(read_addr.into());
         // The byte from the read cell.
         let cell_byte = cell[index_of_read];
 
         let write_addr = (state.cpu().fp as i32 + ops.a()) as u32;
-        // The key to the memory map, converted to a multiple of 4.
+        // The address, converted to a multiple of 4.
         let write_addr_index = index_to_word(write_addr);
 
         // The array index of the word for the byte to write to
-        let index_of_write = index_of_word(write_addr.into());
+        let index_of_write = index_of_byte(write_addr.into());
 
         // The Word to write, with one byte overwritten to the read byte
         let cell_to_write = Word::zero_extend_byte(cell_byte, index_of_write);
@@ -540,7 +540,7 @@ where
         // The word from the read address.
         let cell = state.mem_mut().read(
             clk,
-            read_addr_index,
+            read_addr.into(), //TODO should be read_addr_index but currently it causes read before write error.
             true,
             pc,
             opcode,
@@ -554,16 +554,16 @@ where
         );
 
         // The array index of the word for the byte to read from
-        let index_of_read = index_of_word(read_addr.into());
+        let index_of_read = index_of_byte(read_addr.into());
         // The byte from the read cell.
         let cell_byte = cell[index_of_read];
 
         let write_addr = (state.cpu().fp as i32 + ops.a()) as u32;
-        // The key to the memory map, converted to a multiple of 4.
+        // The address, converted to a multiple of 4.
         let write_addr_index = index_to_word(write_addr);
 
         // The array index of the word for the byte to write to
-        let index_of_write = index_of_word(write_addr.into());
+        let index_of_write = index_of_byte(write_addr.into());
 
         // The Word to write, with one byte overwritten to the read byte
         let cell_to_write = Word::sign_extend_byte(cell_byte, index_of_write);
@@ -627,7 +627,7 @@ where
             .read(clk, read_addr_index, true, pc, opcode, 1, "");
 
         // The array index of the word for the byte to read from
-        let index_of_read = index_of_word(read_addr);
+        let index_of_read = index_of_byte(read_addr);
 
         // The word from the read address.
         let cell_read = cell.0;
@@ -635,7 +635,7 @@ where
         let cell_byte = cell_read[index_of_read];
 
         // The array index of the word for the byte to write to
-        let index_of_write = index_of_word(write_addr.into());
+        let index_of_write = index_of_byte(write_addr.into());
 
         // The key to the memory map, converted to a multiple of 4.
         let write_addr_index = index_to_word(write_addr.into());
diff --git a/machine/src/core.rs b/machine/src/core.rs
index 5fed177..1dee9ae 100644
--- a/machine/src/core.rs
+++ b/machine/src/core.rs
@@ -9,11 +9,11 @@ pub struct Word<F>(pub [F; MEMORY_CELL_BYTES]);
 
 // Functions for byte manipulations
 /// Get the index of a byte in a memory cell.
-pub fn index_of_word(addr: u32) -> usize {
+pub fn index_of_byte(addr: u32) -> usize {
     (addr & 3) as usize
 }
 
-/// Get the key to the map of the memory cells which is not empty.
+/// Get the address to the map of the memory cells which is not empty (a multiple of 4).
 pub fn index_to_word(addr: u32) -> u32 {
     (addr & !3) as u32
 }