diff --git a/tljh/apt.py b/tljh/apt.py
index 85d3f3a..4612958 100644
--- a/tljh/apt.py
+++ b/tljh/apt.py
@@ -26,11 +26,11 @@ def add_source(name, source_url, section):
     """
     # lsb_release is not installed in most docker images by default
     distro = subprocess.check_output(['/bin/bash', '-c', 'source /etc/os-release && echo ${VERSION_CODENAME}'], stderr=subprocess.STDOUT).decode().strip()
-    line = f'deb {source_url} {distro} {section}'
+    line = f'deb {source_url} {distro} {section}\n'
     with open(os.path.join('/etc/apt/sources.list.d/', name + '.list'), 'a+') as f:
         # Write out deb line only if it already doesn't exist
-        if f.read() != line:
-            f.seek(0)
+        f.seek(0)
+        if line not in f.read():
             f.write(line)
             f.truncate()
             utils.run_subprocess(['apt-get', 'update', '--yes'])