diff --git a/crates/rrg/Cargo.toml b/crates/rrg/Cargo.toml
index e6d0e235..a2a7a31b 100644
--- a/crates/rrg/Cargo.toml
+++ b/crates/rrg/Cargo.toml
@@ -124,6 +124,9 @@ version = "0.8.5"
 [dev-dependencies.tempfile]
 version = "3.13.0"
 
+[dev-dependencies.quickcheck]
+version = "1.0.3"
+
 [target.'cfg(target_family = "windows")'.dev-dependencies.windows-sys]
 version = "0.59.0"
 features = [
diff --git a/crates/rrg/src/action/grep_file_contents.rs b/crates/rrg/src/action/grep_file_contents.rs
index 66039171..b97ce198 100644
--- a/crates/rrg/src/action/grep_file_contents.rs
+++ b/crates/rrg/src/action/grep_file_contents.rs
@@ -29,18 +29,17 @@ where
     let file = std::fs::File::open(&args.path)
         .map_err(crate::session::Error::action)?;
 
-    let mut file = std::io::BufReader::new(file);
+    let mut file = crate::io::LineReader::new(file)
+        // We want to support lines only up to 1 MiB. Fleetspeak does not allow
+        // for messages bigger than 2 MiB anyway.
+        .with_max_line_len(1 * 1024 * 1024);
 
-    // TODO(@panhania): Read to a buffer of predefined size so that we do not
-    // allow reading lines of arbitrary length.
     let mut line = String::new();
     let mut offset = 0;
 
     loop {
-        use std::io::BufRead as _;
-
         line.clear();
-        let len = match file.read_line(&mut line) {
+        let len = match file.read_line_lossy(&mut line) {
             Ok(0) => return Ok(()),
             Ok(len) => len,
             Err(error) => return Err(crate::session::Error::action(error)),
diff --git a/crates/rrg/src/io.rs b/crates/rrg/src/io.rs
index 89f08940..a169a037 100644
--- a/crates/rrg/src/io.rs
+++ b/crates/rrg/src/io.rs
@@ -75,6 +75,139 @@ where
     Ok(written)
 }
 
+/// Buffered reader for efficent line reading.
+///
+/// This object works similarly to [`std::io::BufReader`] but is tailored for
+/// line reading capabilities.
+pub struct LineReader<R: Read> {
+    /// Content source to read from.
+    inner: R,
+    /// Buffer that we use for reading.
+    buf: Box<[u8]>,
+    /// Number of elements of `buf` that are actually available.
+    buf_fill_len: usize,
+    /// Limit on the length of a single line that the reader can read.
+    max_line_len: usize,
+}
+
+impl<R: Read> LineReader<R> {
+
+    /// Creates a new `LineReader` with default buffer capacity.
+    ///
+    /// See also [`std::io::BufReader::new`].
+    pub fn new(inner: R) -> LineReader<R> {
+        LineReader::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `LineReader` with the specified buffer capacity.
+    ///
+    /// See also [`std::io::BufReader::with_capacity`].
+    pub fn with_capacity(capacity: usize, inner: R) -> LineReader<R> {
+        LineReader {
+            inner,
+            buf: vec![0; capacity].into_boxed_slice(),
+            buf_fill_len: 0,
+            max_line_len: usize::MAX,
+        }
+    }
+
+    /// Sets the limit on the length of a single line that the reader can read.
+    ///
+    /// This is useful to avoid situation in which a large file without any line
+    /// feed characters can cause the memory to be completely exhausted when
+    /// trying to read the line.
+    pub fn with_max_line_len(mut self, len: usize) -> LineReader<R> {
+        self.max_line_len = len;
+        self
+    }
+
+    /// Reads all bytes until a newline (the `0xA` byte) is reached, and appends
+    /// them to the provided `String` buffer.
+    ///
+    /// Unlike [`std::io::BufRead::read_line`], this method does not fail when
+    /// an invalid UTF-8 sequence is encountered but instead uses [lossy UTF-8
+    /// conversion][1], which replaces such sequences with [`U+FFFD REPLACEMENT
+    /// CHARACTER`][2].
+    ///
+    /// # Errors
+    ///
+    /// This function will fail if an I/O error is raised when reading data. In
+    /// such cases `buf` may contain some new bytes that were read so far.
+    ///
+    /// This will also fail if the line length limit was specified and the line
+    /// being read exceeds it.
+    ///
+    /// [1]: std::string::String::from_utf8_lossy
+    /// [2]: std::char::REPLACEMENT_CHARACTER
+    pub fn read_line_lossy(&mut self, buf: &mut String) -> std::io::Result<usize> {
+        let mut len = 0;
+
+        loop {
+            // We may have a line feed somewhere in our buffer already. In such
+            // a case, we extend the result buffer with content up until that
+            // point (provided that the length limit is not exceeted) and
+            // advance the internal buffer accordingly.
+            if let Some(pos) = self.buf[..self.buf_fill_len].iter().position(|byte| *byte == b'\n') {
+                if len + pos + 1 > self.max_line_len {
+                    return Err(std::io::Error::other(MaxLineLenError(self.max_line_len)));
+                }
+
+                buf.push_str(&String::from_utf8_lossy(&self.buf[..pos + 1]));
+                len += pos + 1;
+
+                self.buf.rotate_left(pos + 1);
+                self.buf_fill_len -= pos + 1;
+                return Ok(len);
+            }
+
+            // There is no line feed in our buffer. Thus, we put everything we
+            // have to the result string (provided that the length limit is not
+            // exceeded) and fill it again with new content.
+
+            if len + self.buf_fill_len > self.max_line_len {
+                return Err(std::io::Error::other(MaxLineLenError(self.max_line_len)));
+            }
+
+            buf.push_str(&String::from_utf8_lossy(&self.buf[..self.buf_fill_len]));
+            len += self.buf_fill_len;
+
+            self.buf_fill_len = 0;
+            loop {
+                match self.inner.read(&mut self.buf) {
+                    Ok(0) => {
+                        // We reached the end of the input without finding any
+                        // line feed character.
+                        return Ok(len);
+                    }
+                    Ok(len) => {
+                        self.buf_fill_len = len;
+                        break;
+                    }
+                    Err(error) if error.kind() == std::io::ErrorKind::Interrupted => {
+                        // We do what the standard library does in case reads to a
+                        // buffer fail with interruption errors: we try again.
+                        continue;
+                    }
+                    Err(error) => return Err(error),
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+struct MaxLineLenError(usize);
+
+impl std::fmt::Display for MaxLineLenError {
+
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "maximum line length ({} bytes) exceeded", self.0)
+    }
+}
+
+impl std::error::Error for MaxLineLenError {
+}
+
 /// An reader implementation for a stream of readers.
 ///
 /// It turns a stream of `Read` instances into one `Read` instance where bytes
@@ -150,6 +283,8 @@ mod tests {
 
     use super::*;
 
+    use quickcheck::quickcheck;
+
     #[test]
     fn test_copy_until_with_empty_buffer() {
         let mut reader: &[u8] = b"";
@@ -199,6 +334,193 @@ mod tests {
         assert!(writer.len() > limit);
     }
 
+    #[test]
+    fn line_reader_empty() {
+        let mut reader = LineReader::new("".as_bytes());
+        let mut line = String::new();
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 0);
+        assert_eq!(line, "");
+    }
+
+    #[test]
+    fn line_reader_one_line_without_line_feed() {
+        let mut reader = LineReader::new("foo".as_bytes());
+        let mut line = String::new();
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 3);
+        assert_eq!(line, "foo");
+    }
+
+    #[test]
+    fn line_reader_one_line_with_line_feed() {
+        let mut reader = LineReader::new("foo\n".as_bytes());
+        let mut line = String::new();
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "foo\n");
+    }
+
+    #[test]
+    fn line_reader_many_lines() {
+        let mut reader = LineReader::new("foo\nbar\nbaz".as_bytes());
+        let mut line = String::new();
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "foo\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "bar\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 3);
+        assert_eq!(line, "baz");
+    }
+
+    #[test]
+    fn line_reader_small_capacity_one_line_without_line_feed() {
+        let mut reader = LineReader::with_capacity(2, "quux".as_bytes());
+        let mut line = String::new();
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "quux");
+    }
+
+    #[test]
+    fn line_reader_small_capacity_one_line_with_line_feed() {
+        let mut reader = LineReader::with_capacity(2, "quux\n".as_bytes());
+        let mut line = String::new();
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 5);
+        assert_eq!(line, "quux\n");
+    }
+
+    #[test]
+    fn line_reader_small_capacity_many_lines() {
+        let mut reader = LineReader::with_capacity(2, "foo\nbar\nbaz".as_bytes());
+        let mut line = String::new();
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "foo\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "bar\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 3);
+        assert_eq!(line, "baz");
+    }
+
+    #[test]
+    fn line_reader_small_max_line_len_one_line_without_line_feed() {
+        let mut reader = LineReader::new("foo".as_bytes())
+            .with_max_line_len(2);
+
+        let error = reader.read_line_lossy(&mut String::new())
+            .unwrap_err().into_inner().unwrap()
+            .downcast::<MaxLineLenError>().unwrap();
+        assert!(matches!(error.as_ref(), MaxLineLenError(2)));
+    }
+
+    #[test]
+    fn line_reader_small_max_line_len_one_line_with_line_feed() {
+        let mut reader = LineReader::new("foo\n".as_bytes())
+            .with_max_line_len(3);
+
+        let error = reader.read_line_lossy(&mut String::new())
+            .unwrap_err().into_inner().unwrap()
+            .downcast::<MaxLineLenError>().unwrap();
+        assert!(matches!(error.as_ref(), MaxLineLenError(3)));
+    }
+
+    #[test]
+    fn line_reader_invalid_utf8_without_line_feed() {
+        let mut reader = LineReader::new(&b"ba\xF0\x90\x80"[..]);
+        let mut line = String::new();
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 5);
+        assert_eq!(line, "ba�");
+    }
+
+    #[test]
+    fn line_reader_invalid_utf8_with_line_feed() {
+        let mut reader = LineReader::new(&b"ba\xF0\x90\x80\n"[..]);
+        let mut line = String::new();
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 6);
+        assert_eq!(line, "ba�\n");
+    }
+
+    #[test]
+    fn line_reader_append() {
+        let mut reader = LineReader::new("content".as_bytes());
+        let mut line = String::from("prefix");
+
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 7);
+        assert_eq!(line, "prefixcontent");
+    }
+
+    #[test]
+    fn line_reader_empty_lines() {
+        let mut reader = LineReader::new("\n\nfoo\n\n".as_bytes());
+        let mut line = String::new();
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 1);
+        assert_eq!(line, "\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 1);
+        assert_eq!(line, "\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 4);
+        assert_eq!(line, "foo\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 1);
+        assert_eq!(line, "\n");
+
+        line.clear();
+        assert_eq!(reader.read_line_lossy(&mut line).unwrap(), 0);
+        assert_eq!(line, "");
+    }
+
+    quickcheck! {
+
+        fn line_reader_joined_lines(strings: Vec<String>) -> quickcheck::TestResult {
+            // This property holds only for strings without line feed chars as
+            // otherwise an input string can get an extra split when reading.
+            if strings.iter().any(|string| string.contains('\n')) {
+                return quickcheck::TestResult::discard();
+            }
+
+            let mut content = strings.join("\n");
+            content.push('\n');
+
+            let mut reader = LineReader::new(content.as_bytes());
+            let mut line = String::new();
+
+            for string in &strings {
+                line.clear();
+                if reader.read_line_lossy(&mut line).unwrap() != string.len() + 1 {
+                    return quickcheck::TestResult::failed();
+                }
+                if line != format!("{string}\n") {
+                    return quickcheck::TestResult::failed();
+                }
+            }
+
+            quickcheck::TestResult::passed()
+        }
+    }
+
     #[test]
     fn test_iter_reader_with_empty_iter() {
         let mut reader = IterReader::new(std::iter::empty::<&[u8]>());