diff --git a/src/fox32.pest b/src/fox32.pest
index bb4fcaa..5157327 100644
--- a/src/fox32.pest
+++ b/src/fox32.pest
@@ -122,13 +122,13 @@ instruction_two = @{
 }
 
 immediate_bin  = ${ "0b" ~ body_bin }
-body_bin       = @{ ASCII_BIN_DIGIT+ }
+body_bin       = @{ (ASCII_BIN_DIGIT | "_")+ }
 
 immediate_hex  = ${ "0x" ~ body_hex }
-body_hex       = @{ ASCII_HEX_DIGIT+ }
+body_hex       = @{ (ASCII_HEX_DIGIT | "_")+ }
 
 immediate_dec  = ${ body_dec }
-body_dec       = @{ ASCII_DIGIT+ }
+body_dec       = @{ (ASCII_DIGIT | "_")+ }
 
 immediate_char = ${ "'" ~ body_char ~ "'" }
 body_char      = @{ '\x00'..'\x7F' }
diff --git a/src/main.rs b/src/main.rs
index 9c02e63..1519850 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -602,6 +602,10 @@ fn parse_instruction(pair: pest::iterators::Pair<Rule>) -> AstNode {
     }
 }
 
+fn remove_underscores(input: &str) -> String {
+    String::from_iter(input.chars().filter(|c| *c != '_'))
+}
+
 fn parse_operand(mut pair: pest::iterators::Pair<Rule>, is_pointer: bool) -> AstNode {
     //println!("parse_operand: {:#?}", pair); // debug
     let size = *CURRENT_SIZE.lock().unwrap();
@@ -616,7 +620,7 @@ fn parse_operand(mut pair: pest::iterators::Pair<Rule>, is_pointer: bool) -> Ast
             match operand_value_pair.as_rule() {
                 Rule::immediate_bin => {
                     let body_bin_str = operand_value_pair.into_inner().next().unwrap().as_str();
-                    let immediate = u32::from_str_radix(body_bin_str, 2).unwrap();
+                    let immediate = u32::from_str_radix(&remove_underscores(body_bin_str), 2).unwrap();
                     if is_pointer {
                         AstNode::ImmediatePointer(immediate)
                     } else {
@@ -629,7 +633,7 @@ fn parse_operand(mut pair: pest::iterators::Pair<Rule>, is_pointer: bool) -> Ast
                 }
                 Rule::immediate_hex => {
                     let body_hex_str = operand_value_pair.into_inner().next().unwrap().as_str();
-                    let immediate = u32::from_str_radix(body_hex_str, 16).unwrap();
+                    let immediate = u32::from_str_radix(&remove_underscores(body_hex_str), 16).unwrap();
                     if is_pointer {
                         AstNode::ImmediatePointer(immediate)
                     } else {
@@ -642,7 +646,7 @@ fn parse_operand(mut pair: pest::iterators::Pair<Rule>, is_pointer: bool) -> Ast
                 }
                 Rule::immediate_dec => {
                     let body_dec_str = operand_value_pair.into_inner().next().unwrap().as_str();
-                    let immediate = body_dec_str.parse::<u32>().unwrap();
+                    let immediate = remove_underscores(body_dec_str).parse::<u32>().unwrap();
                     if is_pointer {
                         AstNode::ImmediatePointer(immediate)
                     } else {