diff --git a/include/pocketpy/compiler.h b/include/pocketpy/compiler.h
index 6daa785b..6f491892 100644
--- a/include/pocketpy/compiler.h
+++ b/include/pocketpy/compiler.h
@@ -135,7 +135,7 @@ struct TokenDeserializer{
 
     std::string_view read_string(char c);
     Str read_string_from_hex(char c);
-    i64 read_int(char c);
+    i64 read_uint(char c);
     f64 read_float(char c);
 };
 
diff --git a/include/pocketpy/lexer.h b/include/pocketpy/lexer.h
index 8cd51fbd..ff268454 100644
--- a/include/pocketpy/lexer.h
+++ b/include/pocketpy/lexer.h
@@ -139,6 +139,6 @@ enum class IntParsingResult{
     Overflow,
 };
 
-IntParsingResult parse_int(std::string_view text, i64* out, int base);
+IntParsingResult parse_uint(std::string_view text, i64* out, int base);
 
 } // namespace pkpy
diff --git a/src/compiler.cpp b/src/compiler.cpp
index b2927219..ba91e8a7 100644
--- a/src/compiler.cpp
+++ b/src/compiler.cpp
@@ -1281,29 +1281,29 @@ __EAT_DOTS_END:
         if(version != PK_VERSION){
             SyntaxError(_S("precompiled version mismatch: ", version, "!=" PK_VERSION));
         }
-        if(deserializer.read_int('\n') != (i64)mode()){
+        if(deserializer.read_uint('\n') != (i64)mode()){
             SyntaxError("precompiled mode mismatch");
         }
         
         lexer.src->_precompiled_tokens = deserializer.read_string('\n');
         deserializer.curr += 1;     // skip '='
-        i64 count = deserializer.read_int('\n');
+        i64 count = deserializer.read_uint('\n');
         const char* tokens_c_str = lexer.src->_precompiled_tokens.c_str();
         for(int i=0; i<count; i++){
             Token t;
-            t.type = (unsigned char)deserializer.read_int(',');
+            t.type = (unsigned char)deserializer.read_uint(',');
             if(is_raw_string_used(t.type)){
-                t.start = tokens_c_str + deserializer.read_int(',');
-                t.length = deserializer.read_int(',');
+                t.start = tokens_c_str + deserializer.read_uint(',');
+                t.length = deserializer.read_uint(',');
             }else{
                 t.start = nullptr;
                 t.length = 0;
             }
-            t.line = (int)deserializer.read_int(',');
-            t.brackets_level = (int)deserializer.read_int(',');
+            t.line = (int)deserializer.read_uint(',');
+            t.brackets_level = (int)deserializer.read_uint(',');
             char type = deserializer.read_char();
             switch(type){
-                case 'I': t.value = deserializer.read_int('\n'); break;
+                case 'I': t.value = deserializer.read_uint('\n'); break;
                 case 'F': t.value = deserializer.read_float('\n'); break;
                 case 'S': t.value = deserializer.read_string_from_hex('\n'); break;
                 default: t.value = {}; break;
@@ -1385,11 +1385,13 @@ __EAT_DOTS_END:
         return std::pair<char*, int>(buffer, s.size()/2);
     }
 
-    i64 TokenDeserializer::read_int(char c){
-        std::string_view sv = read_string(c);
-        i64 out;
-        IntParsingResult res = parse_int(sv, &out, 10);
-        PK_ASSERT(res == IntParsingResult::Success);
+    i64 TokenDeserializer::read_uint(char c){
+        i64 out = 0;
+        while(*curr != c){
+            out = out*10 + (*curr-'0');
+            curr++;
+        }
+        curr++;     // skip the delimiter
         return out;
     }
 
diff --git a/src/lexer.cpp b/src/lexer.cpp
index 64384827..918dec48 100644
--- a/src/lexer.cpp
+++ b/src/lexer.cpp
@@ -292,7 +292,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
             }
             // try integer
             i64 int_out;
-            switch(parse_int(text, &int_out, -1)){
+            switch(parse_uint(text, &int_out, -1)){
                 case IntParsingResult::Success:
                     add_token(TK("@num"), int_out);
                     return;
@@ -491,13 +491,13 @@ static bool is_unicode_Lo_char(uint32_t c) {
         return std::move(nexts);
     }
 
-IntParsingResult parse_int(std::string_view text, i64* out, int base){
-  *out = 0;
-
-  const auto f_startswith_2 = [](std::string_view t, const char* prefix) -> bool{
+inline constexpr bool f_startswith_2(std::string_view t, const char* prefix){
     if(t.length() < 2) return false;
     return t[0] == prefix[0] && t[1] == prefix[1];
-  };
+}
+
+IntParsingResult parse_uint(std::string_view text, i64* out, int base){
+  *out = 0;
 
   if(base == -1){
     if(f_startswith_2(text, "0b")) base = 2;
diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index b3962679..90647f27 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -443,7 +443,7 @@ void init_builtins(VM* _vm) {
             sv.remove_prefix(1);
         }
         i64 val;
-        if(parse_int(sv, &val, base) != IntParsingResult::Success){
+        if(parse_uint(sv, &val, base) != IntParsingResult::Success){
             vm->ValueError(_S("invalid literal for int() with base ", base, ": ", s.escape()));
         }
         if(negative) val = -val;