diff --git a/ghostscope-compiler/src/script/grammar.pest b/ghostscope-compiler/src/script/grammar.pest
index fae1556..a7ceb6e 100644
--- a/ghostscope-compiler/src/script/grammar.pest
+++ b/ghostscope-compiler/src/script/grammar.pest
@@ -113,7 +113,7 @@ address_of = { "&" ~ ( "(" ~ expr ~ ")" | complex_variable | identifier ) }
 add_op = { "+" | "-" }
 mul_op = { "*" | "/" }
 
-identifier = @{ ASCII_ALPHA ~ (ASCII_ALPHANUMERIC | "_")* }
+identifier = @{ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")* }
 // Integer literals
 int = @{ ASCII_DIGIT+ }
 hex_int = @{ "0x" ~ ASCII_HEX_DIGIT+ }
diff --git a/ghostscope-compiler/src/script/parser.rs b/ghostscope-compiler/src/script/parser.rs
index 0b97873..7a00ed8 100644
--- a/ghostscope-compiler/src/script/parser.rs
+++ b/ghostscope-compiler/src/script/parser.rs
@@ -2058,6 +2058,23 @@ trace foo {
         assert!(parse(s5).is_ok());
     }
 
+    #[test]
+    fn parse_identifiers_can_start_with_underscore() {
+        let function = r#"trace __UpdateTicketInformation { print "OK"; }"#;
+        assert!(parse(function).is_ok());
+
+        let wildcard = r#"trace __builtin_* { print "W"; }"#;
+        assert!(parse(wildcard).is_ok());
+
+        let script = r#"
+trace _start {
+    let _ticket = __dwarf_value;
+    print _ticket;
+}
+"#;
+        assert!(parse(script).is_ok());
+    }
+
     #[test]
     fn parse_module_hex_address_overflow_should_error() {
         // Address exceeds u64 (17 hex digits) -> parse error, not 0 fallback