diff --git a/ghostscope-compiler/src/script/parser/diagnostics.rs b/ghostscope-compiler/src/script/parser/diagnostics.rs
index ec812569..5d081e8f 100644
--- a/ghostscope-compiler/src/script/parser/diagnostics.rs
+++ b/ghostscope-compiler/src/script/parser/diagnostics.rs
@@ -1,3 +1,6 @@
+use super::{GhostScopeParser, Rule};
+use pest::Parser;
+
 // Best-effort heuristic: if a line contains a print statement with an opening quote
 // but no closing quote before arguments, give a clearer error.
 pub(super) fn detect_unclosed_print_string(input: &str) -> Option<String> {
@@ -100,6 +103,55 @@ pub(super) fn detect_unknown_keyword(input: &str) -> Option<String> {
         dp[idx(n, m)]
     }
 
+    fn double_slash_is_in_trace_path(
+        line: &str,
+        statement_start: usize,
+        slash_start: usize,
+    ) -> bool {
+        let statement = &line[statement_start..];
+        let statement = statement.trim_start();
+        let statement_start = line.len() - statement.len();
+        let Some(after_trace) = statement.strip_prefix("trace") else {
+            return false;
+        };
+        if !after_trace.starts_with(char::is_whitespace) {
+            return false;
+        }
+
+        let pattern = after_trace.trim_start();
+        let pattern_start = statement_start + statement.len() - pattern.len();
+        let Some(block_start) = pattern.find('{') else {
+            return false;
+        };
+        let pattern = pattern[..block_start].trim_end();
+
+        let Ok(mut pairs) = GhostScopeParser::parse(Rule::trace_pattern, pattern) else {
+            return false;
+        };
+        let Some(trace_pattern) = pairs.next() else {
+            return false;
+        };
+        if trace_pattern.as_span().end() != pattern.len() {
+            return false;
+        }
+        let Some(path_pattern) = trace_pattern.into_inner().next() else {
+            return false;
+        };
+        if !matches!(
+            path_pattern.as_rule(),
+            Rule::source_line | Rule::module_hex_address
+        ) {
+            return false;
+        }
+        let Some(file_path) = path_pattern.into_inner().next() else {
+            return false;
+        };
+        let path_start = pattern_start + file_path.as_span().start();
+        let path_end = pattern_start + file_path.as_span().end();
+
+        path_start < slash_start && slash_start + 1 < path_end
+    }
+
     // Helper: check a slice for a command-like unknown keyword
     fn check_slice(slice: &str, line_no_1based: usize) -> Option<String> {
         let mut s = slice.trim_start();
@@ -190,10 +242,16 @@ pub(super) fn detect_unknown_keyword(input: &str) -> Option<String> {
 
     for (i, raw_line) in input.lines().enumerate() {
         let line = raw_line;
-        // Scan potential statement starts: at line start, and right after '{', ';', '}', '(', ',' (outside strings)
+        // Scan potential statement starts: at line start, and right after '{', ';', '}', '(', ',' (outside strings and comments)
         let mut quote_open = false;
         let mut positions: Vec<usize> = vec![0]; // include start-of-line
         for (idx, ch) in line.char_indices() {
+            if !quote_open
+                && line[idx..].starts_with("//")
+                && !double_slash_is_in_trace_path(line, positions.last().copied().unwrap_or(0), idx)
+            {
+                break;
+            }
             if ch == '"' {
                 quote_open = !quote_open;
             }
diff --git a/ghostscope-compiler/src/script/parser/tests.rs b/ghostscope-compiler/src/script/parser/tests.rs
index bab54492..df6879ea 100644
--- a/ghostscope-compiler/src/script/parser/tests.rs
+++ b/ghostscope-compiler/src/script/parser/tests.rs
@@ -1244,3 +1244,32 @@ foobarbaz {
         other => panic!("expected friendly SyntaxError with expected list, got {other:?}"),
     }
 }
+
+#[test]
+fn parse_error_ignores_commas_in_line_comments() {
+    let s = "trace foo {\n    // explain the output, including ignored words\n    print somevalue -> other;\n}";
+    let r = parse(s);
+    match r {
+        Err(err @ ParseError::Pest(_)) => {
+            let msg = err.to_string();
+            assert!(
+                msg.contains("Pest parser error:  --> 3:22"),
+                "unexpected error location: {msg}"
+            );
+        }
+        other => panic!("expected Pest error at '->', got {other:?}"),
+    }
+}
+
+#[test]
+fn parse_unknown_keyword_after_trace_path_with_double_slash() {
+    let s = r#"trace /foo//bar.c:1 { prnit "x"; }"#;
+    let r = parse(s);
+    match r {
+        Err(ParseError::SyntaxError(msg)) => {
+            assert!(msg.contains("Unknown keyword 'prnit'"), "{msg}");
+            assert!(msg.contains("Did you mean 'print'"), "{msg}");
+        }
+        other => panic!("expected friendly SyntaxError after trace path, got {other:?}"),
+    }
+}