diff --git a/CMakeLists.txt b/CMakeLists.txt
index 67a0e8a6..8a0a6160 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -79,4 +79,12 @@ endif()
 
 if(PK_EXPORT_CXX_SYMBOLS AND MSVC)
     set_target_properties(${PROJECT_NAME} PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS ON)
-endif()
\ No newline at end of file
+endif()
+
+# enable link time optimization
+include(CheckIPOSupported)
+check_ipo_supported(RESULT result)
+if(result)
+    message(STATUS "LTO enabled")
+    set_target_properties(${PROJECT_NAME} PROPERTIES INTERPROCEDURAL_OPTIMIZATION TRUE)
+endif()
diff --git a/src/lexer.cpp b/src/lexer.cpp
index 8c5eae45..924bfe31 100644
--- a/src/lexer.cpp
+++ b/src/lexer.cpp
@@ -283,7 +283,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
 
         int base = 10;
         if (m[1].matched) {
-            char tag = m[1].first.base()[1];
+            char tag = m[1].first[1];
             switch (tag) {
                 case 'x': base = 16; break;
                 case 'o': base = 8; break;
@@ -303,7 +303,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
             }
             add_token(TK("@num"), out);
         } else {
-            std::string_view text(m[0].first.base(), m[0].length());
+            std::string_view text(&m[0].first[0], m[0].length());
             i64 out;
             bool ok = parse_int(text, &out, base);
             if(!ok){
diff --git a/tests/01_int.py b/tests/01_int.py
index 3a27aeb4..a5aa7ff3 100644
--- a/tests/01_int.py
+++ b/tests/01_int.py
@@ -2,16 +2,23 @@
 assert 0xffff == 65535
 assert 0xAAFFFF == 11206655
 assert 0x7fffffff == 2147483647
+assert -0xffff == -65535
+assert -0xAAFFFF == -11206655
+assert -0x7fffffff == -2147483647
 # test 64-bit
 assert 2**60-1 + 546 - 0xfffffffffffff == 1148417904979477026
 
 # test oct literals
 assert 0o1234 == 668
 assert 0o17777777777 == 2147483647
+assert -0o1234 == -668
+assert -0o17777777777 == -2147483647
 
 # test binary literals
 assert 0b10010 == 18
+assert -0b10010 == -18
 assert 0b11111111111111111111111111111111 == 4294967295
+assert -0b11111 == -31
 
 # test == != >= <= < >
 assert -1 == -1