diff --git a/Cargo.toml b/Cargo.toml
index 30d62dc..4be34f4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,16 +5,20 @@ edition = "2021"
 
 [dependencies]
 anyhow = "1.0"
-regex = "1.10"
-ureq = "2.10"
-kxio = "1.2"
-ignore = "0.4"
 bon = "2.3"
-tokio = { version = "1.37", features = [ "full" ] }
-serde = { version = "1.0", features = [ "derive" ] }
+ignore = "0.4"
+file-format = { version = "0.25", features = ["reader-txt"] }
+kxio = "1.2"
+regex = "1.10"
+serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+tokio = { version = "1.37", features = ["full"] }
+ureq = "2.10"
 
 [dev-dependencies]
 assert2 = "0.3"
 pretty_assertions = "1.4"
 rstest = "0.22"
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(tarpaulin_include)'] }
diff --git a/src/issues/fetch.rs b/src/issues/fetch.rs
index 63bcba6..b10fd23 100644
--- a/src/issues/fetch.rs
+++ b/src/issues/fetch.rs
@@ -23,7 +23,7 @@ pub async fn fetch_open_issues(config: &Config) -> Result<HashSet<Issue>> {
     let issues: HashSet<Issue> = config
         .net()
         .get::<Vec<Issue>>(request)
-        .await?
+        .await? // tarpaulin uncovered okay
         .response_body()
         .unwrap_or_default()
         .into_iter()
diff --git a/src/main.rs b/src/main.rs
index 088743a..bd0757c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,7 +2,7 @@
 use anyhow::{bail, Result};
 use init::init_config;
 use issues::fetch_open_issues;
-use scanner::find_markers;
+use scanner::{find_markers, DefaultFileScanner};
 
 mod init;
 mod issues;
@@ -14,6 +14,7 @@ mod scanner;
 mod tests;
 
 #[tokio::main]
+#[cfg(not(tarpaulin_include))]
 async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
     Ok(run(kxio::network::Network::new_real()).await?)
 }
@@ -23,7 +24,7 @@ async fn run(net: kxio::network::Network) -> Result<()> {
 
     let config = init_config(net)?;
     let issues = fetch_open_issues(&config).await?;
-    let markers = find_markers(&config, issues)?;
+    let markers = find_markers(&config, issues, &DefaultFileScanner)?;
 
     let mut errors = false;
     for marker in (*markers).iter() {
diff --git a/src/model/markers/mod.rs b/src/model/markers/mod.rs
index e392629..afb44ac 100644
--- a/src/model/markers/mod.rs
+++ b/src/model/markers/mod.rs
@@ -19,6 +19,7 @@ impl Marker {
     pub fn into_closed(self) -> Self {
         match self {
             Self::Valid(line, issue) => Self::Closed(line, issue),
+            #[cfg(not(tarpaulin_include))] // only ever called when is a Valid
             _ => self,
         }
     }
diff --git a/src/scanner.rs b/src/scanner.rs
index d16d436..36ec1d7 100644
--- a/src/scanner.rs
+++ b/src/scanner.rs
@@ -6,46 +6,72 @@ use crate::{
     model::{Config, Line, Marker, Markers},
 };
 use anyhow::Result;
+use file_format::FileFormat;
 use ignore::Walk;
 
-pub fn find_markers(config: &Config, issues: HashSet<Issue>) -> Result<Markers, anyhow::Error> {
+//<'a> = dyn Fn(&'a Path, &'a Config, &'a mut Markers, &'a HashSet<Issue>, Output=Result<()>);
+pub trait FileScanner {
+    fn scan_file(
+        &self,
+        path: &Path,
+        config: &Config,
+        markers: &mut Markers,
+        issues: &HashSet<Issue>,
+    ) -> Result<()>;
+}
+
+pub fn find_markers(
+    config: &Config,
+    issues: HashSet<Issue>,
+    file_scanner: &impl FileScanner,
+) -> Result<Markers, anyhow::Error> {
     let mut markers = Markers::default();
     for file in Walk::new(config.fs().base()).flatten() {
         let path = file.path();
-        if config.fs().path_is_file(path)? {
-            // TODO: (#4) ignore non-text files
-            scan_file(path, config, &mut markers, &issues)?;
+        if is_text_file(config, path)? {
+            file_scanner.scan_file(path, config, &mut markers, &issues)?
         }
     }
     Ok(markers)
 }
 
-fn scan_file(
-    file: &Path,
-    config: &Config,
-    found_markers: &mut Markers,
-    issues: &HashSet<Issue>,
-) -> Result<()> {
-    let relative_path = file.strip_prefix(config.fs().base())?.to_path_buf();
-    config
-        .fs()
-        .file_read_to_string(file)?
-        .lines()
-        .enumerate()
-        .map(|(n, line)| {
-            Line::builder()
-                .file(file.to_path_buf())
-                .relative_path(relative_path.clone())
-                .num(n + 1) // line numbers are not 0-based, but enumerate is
-                .value(line.to_owned())
-                .build()
-        })
-        .filter_map(|line| line.into_marker().ok())
-        .filter(|marker| !matches!(marker, Marker::Unmarked))
-        .map(|marker| has_open_issue(marker, issues))
-        .for_each(|marker| found_markers.add_marker(marker));
+fn is_text_file(config: &Config, path: &Path) -> Result<bool> {
+    Ok(config.fs().path_is_file(path)?
+        && FileFormat::from_file(path)?
+            .media_type()
+            .starts_with("text/"))
+}
 
-    Ok(())
+pub struct DefaultFileScanner;
+impl FileScanner for DefaultFileScanner {
+    fn scan_file(
+        &self,
+        file: &Path,
+        config: &Config,
+        markers: &mut Markers,
+        issues: &HashSet<Issue>,
+    ) -> Result<()> {
+        let relative_path = file.strip_prefix(config.fs().base())?.to_path_buf();
+        config
+            .fs()
+            .file_read_to_string(file)? // tarpaulin uncovered okay
+            .lines()
+            .enumerate()
+            .map(|(n, line)| {
+                Line::builder()
+                    .file(file.to_path_buf())
+                    .relative_path(relative_path.clone())
+                    .num(n + 1) // line numbers are not 0-based, but enumerate is
+                    .value(line.to_owned())
+                    .build()
+            })
+            .filter_map(|line| line.into_marker().ok())
+            .filter(|marker| !matches!(marker, Marker::Unmarked))
+            .map(|marker| has_open_issue(marker, issues))
+            .for_each(|marker| markers.add_marker(marker));
+
+        Ok(())
+    }
 }
 
 fn has_open_issue(marker: Marker, issues: &HashSet<Issue>) -> Marker {
diff --git a/src/tests/scanner.rs b/src/tests/scanner.rs
index 2d5b2b7..8e6ea2a 100644
--- a/src/tests/scanner.rs
+++ b/src/tests/scanner.rs
@@ -1,7 +1,9 @@
+use crate::scanner::FileScanner;
+
 //
 use super::*;
 
-use std::collections::HashSet;
+use std::{cell::RefCell, collections::HashSet, fs::File, io::Write, path::PathBuf};
 
 use issues::Issue;
 use model::Config;
@@ -32,7 +34,7 @@ fn find_markers_in_dir() -> anyhow::Result<()> {
     let issues = HashSet::from_iter(vec![Issue::new(23), Issue::new(43)]);
 
     //when
-    let markers = find_markers(&config, issues)?;
+    let markers = find_markers(&config, issues, &DefaultFileScanner)?;
 
     //then
     assert_eq!(
@@ -53,3 +55,44 @@ fn find_markers_in_dir() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn skips_binary_files() -> Result<()> {
+    //given
+    let fs = kxio::fs::temp()?;
+    let binary_path = fs.base().join("binary_file.bin");
+    let mut binary_file = File::create(binary_path)?;
+    binary_file.write_all(&[0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9])?;
+    let text_path = fs.base().join("text_file.txt");
+    fs.file_write(&text_path, "text contents")?;
+
+    let net = kxio::network::Network::new_mock();
+    let config = a_config(net, fs)?;
+    let issues = HashSet::new();
+    let file_scanner = TestFileScanner::default();
+
+    //when
+    find_markers(&config, issues, &file_scanner)?;
+
+    //then
+    assert_eq!(file_scanner.scanned.take(), vec![text_path]);
+
+    Ok(())
+}
+
+#[derive(Default)]
+struct TestFileScanner {
+    scanned: RefCell<Vec<PathBuf>>,
+}
+impl FileScanner for TestFileScanner {
+    fn scan_file(
+        &self,
+        path: &std::path::Path,
+        _config: &Config,
+        _markers: &mut model::Markers,
+        _issues: &HashSet<Issue>,
+    ) -> Result<()> {
+        self.scanned.borrow_mut().push(path.to_path_buf());
+        Ok(())
+    }
+}