diff --git a/CMakeLists.txt b/CMakeLists.txt
index e7ce5c9..49933ec 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@ project(
     VERSION 0.1.0
     LANGUAGES CXX C)
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_COLOR_DIAGNOSTICS OFF)
 
 find_package(LLVM REQUIRED CONFIG)
diff --git a/src/Lexer/Lexer.cpp b/src/Lexer/Lexer.cpp
index 2569005..b53893f 100644
--- a/src/Lexer/Lexer.cpp
+++ b/src/Lexer/Lexer.cpp
@@ -271,10 +271,12 @@ shared_ptr<Token> Lexer::match(TokenKind kind, string lexme, bool needsSeparator
 shared_ptr<Token> Lexer::matchIntegerDec() {
     int nextIndex = currentIndex;
 
-    while (nextIndex < source.length() && isDecDigit(nextIndex))
+    // Include _ which is not on the first position
+    while (nextIndex < source.length() && (isDecDigit(nextIndex) || (nextIndex > currentIndex && source.at(nextIndex) == '_')))
         nextIndex++;
     
-    if (nextIndex == currentIndex || !isSeparator(nextIndex))
+    // Resulting number shouldn't be empty, should be separated on the right, and _ shouldn't be the last character
+    if (nextIndex == currentIndex || !isSeparator(nextIndex) || source.at(nextIndex-1) == '_')
         return nullptr;
     
     string lexme = source.substr(currentIndex, nextIndex - currentIndex);
@@ -293,10 +295,12 @@ shared_ptr<Token> Lexer::matchIntegerHex() {
     if (source.at(nextIndex++) != '0' || source.at(nextIndex++) != 'x')
         return nullptr;
 
-    while (nextIndex < source.length() && isHexDigit(nextIndex))
+    // Include _ which is not on the first position
+    while (nextIndex < source.length() && (isHexDigit(nextIndex) || (nextIndex > currentIndex+2 && source.at(nextIndex) == '_')))
         nextIndex++;
-    
-    if (nextIndex == currentIndex || !isSeparator(nextIndex))
+
+    // Resulting number shouldn't be empty, should be separated on the right, and _ shouldn't be the last character
+    if (nextIndex == currentIndex+2 || !isSeparator(nextIndex) || source.at(nextIndex-1) == '_')
         return nullptr;
     
     string lexme = source.substr(currentIndex, nextIndex - currentIndex);
@@ -315,10 +319,12 @@ shared_ptr<Token> Lexer::matchIntegerBin() {
     if (source.at(nextIndex++) != '0' || source.at(nextIndex++) != 'b')
         return nullptr;
 
-    while (nextIndex < source.length() && isBinDigit(nextIndex))
+    // Include _ which is not on the first position    
+    while (nextIndex < source.length() && (isBinDigit(nextIndex) || (nextIndex > currentIndex+2 && source.at(nextIndex) == '_')))
         nextIndex++;
     
-    if (nextIndex == currentIndex || !isSeparator(nextIndex))
+    // Resulting number shouldn't be empty, should be separated on the right, and _ shouldn't be the last character
+    if (nextIndex == currentIndex || !isSeparator(nextIndex) || source.at(nextIndex-1) == '_')
         return nullptr;
     
     string lexme = source.substr(currentIndex, nextIndex - currentIndex);
diff --git a/src/Parser/Expression.cpp b/src/Parser/Expression.cpp
index 0622f14..18a2108 100644
--- a/src/Parser/Expression.cpp
+++ b/src/Parser/Expression.cpp
@@ -130,22 +130,28 @@ Expression(ExpressionKind::LITERAL, ValueType::NONE) {
             boolValue = token->getLexme().compare("true") == 0;
             valueType = ValueType::BOOL;
             break;
-        case TokenKind::INTEGER_DEC:
-            sint32Value = stoi(token->getLexme(), nullptr, 10);
+        case TokenKind::INTEGER_DEC: {
+            string numString = token->getLexme();
+            erase(numString, '_');
+            sint32Value = stoi(numString, nullptr, 10);
             valueType = ValueType::SINT32;
             break;
-        case TokenKind::INTEGER_HEX:
-            sint32Value = stoi(token->getLexme(), nullptr, 16);
+        }
+        case TokenKind::INTEGER_HEX: {
+            string numString = token->getLexme();
+            erase(numString, '_');
+            sint32Value = stoi(numString, nullptr, 16);
             valueType = ValueType::SINT32;
             break;
-        case TokenKind::INTEGER_BIN:
-            sint32Value = stoi(
-                token->getLexme().substr(2, token->getLexme().size()-1),
-                nullptr,
-                2
-            );
+        }
+        case TokenKind::INTEGER_BIN: {
+            string numString = token->getLexme();
+            erase(numString, '_');
+            numString = numString.substr(2, numString.size()-1);
+            sint32Value = stoi(numString, nullptr, 2);
             valueType = ValueType::SINT32;
             break;
+        }
         case TokenKind::REAL:
             real32Value = stof(token->getLexme());
             valueType = ValueType::REAL32;