diff --git a/cli/src/main.rs b/cli/src/main.rs
index dc4b5ae6..db403fea 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -54,6 +54,7 @@ fn run() -> error::Result<()> {
                 .arg(Arg::with_name("debug-graph").long("debug-graph").short("D"))
                 .arg(Arg::with_name("quiet").long("quiet").short("q"))
                 .arg(Arg::with_name("time").long("time").short("t"))
+                .arg(Arg::with_name("allow-cancellation").long("cancel"))
                 .arg(Arg::with_name("timeout").long("timeout").takes_value(true)),
         )
         .subcommand(
@@ -134,6 +135,7 @@ fn run() -> error::Result<()> {
         let debug_graph = matches.is_present("debug-graph");
         let quiet = matches.is_present("quiet");
         let time = matches.is_present("time");
+        let allow_cancellation = matches.is_present("allow-cancellation");
         let timeout = matches
             .value_of("timeout")
             .map_or(0, |t| u64::from_str_radix(t, 10).unwrap());
@@ -170,6 +172,7 @@ fn run() -> error::Result<()> {
                 timeout,
                 debug,
                 debug_graph,
+                allow_cancellation,
             )?;
         }
 
diff --git a/cli/src/parse.rs b/cli/src/parse.rs
index f4002233..b5230e77 100644
--- a/cli/src/parse.rs
+++ b/cli/src/parse.rs
@@ -1,9 +1,10 @@
 use super::error::{Error, Result};
 use super::util;
-use std::fs;
 use std::io::{self, Write};
 use std::path::Path;
+use std::sync::atomic::{AtomicU32, Ordering};
 use std::time::Instant;
+use std::{fs, thread};
 use tree_sitter::{Language, LogType, Parser};
 
 pub fn parse_file_at_path(
@@ -15,6 +16,7 @@ pub fn parse_file_at_path(
     timeout: u64,
     debug: bool,
     debug_graph: bool,
+    allow_cancellation: bool,
 ) -> Result<bool> {
     let mut _log_session = None;
     let mut parser = Parser::new();
@@ -22,9 +24,28 @@ pub fn parse_file_at_path(
     let source_code = fs::read(path)
         .map_err(|e| Error(format!("Error reading source file {:?}: {}", path, e)))?;
 
+    // If the `--cancel` flag was passed, then cancel the parse
+    // when the user types a newline.
+    if allow_cancellation {
+        let flag = Box::new(AtomicU32::new(0));
+        unsafe { parser.set_cancellation_flag(Some(&flag)) };
+        thread::spawn(move || {
+            let mut line = String::new();
+            io::stdin().read_line(&mut line).unwrap();
+            eprintln!("Cancelling");
+            flag.store(1, Ordering::Relaxed);
+        });
+    }
+
+    // Set a timeout based on the `--time` flag.
+    parser.set_timeout_micros(timeout);
+
+    // Render an HTML graph if `--debug-graph` was passed
     if debug_graph {
         _log_session = Some(util::log_graphs(&mut parser, "log.html")?);
-    } else if debug {
+    }
+    // Log to stderr if `--debug` was passed
+    else if debug {
         parser.set_logger(Some(Box::new(|log_type, message| {
             if log_type == LogType::Lex {
                 io::stderr().write(b"  ").unwrap();
@@ -33,7 +54,6 @@ pub fn parse_file_at_path(
         })));
     }
 
-    parser.set_timeout_micros(timeout);
     let time = Instant::now();
     let tree = parser.parse(&source_code, None);
     let duration = time.elapsed();
@@ -139,7 +159,7 @@ pub fn parse_file_at_path(
             write!(&mut stdout, "\n")?;
         }
 
-        return Ok(first_error.is_some())
+        return Ok(first_error.is_some());
     } else if print_time {
         writeln!(
             &mut stdout,
diff --git a/lib/src/atomic.h b/lib/src/atomic.h
index 51abccf8..89f40e48 100644
--- a/lib/src/atomic.h
+++ b/lib/src/atomic.h
@@ -22,7 +22,7 @@ static inline uint32_t atomic_dec(volatile uint32_t *p) {
 #else
 
 static inline uint32_t atomic_load(const volatile uint32_t *p) {
-  return __atomic_load_n(p, __ATOMIC_SEQ_CST);
+  return __atomic_load_n(p, __ATOMIC_RELAXED);
 }
 
 static inline uint32_t atomic_inc(volatile uint32_t *p) {