diff --git a/osbuild/util/mnt.py b/osbuild/util/mnt.py
index 7169bd39..828659fb 100644
--- a/osbuild/util/mnt.py
+++ b/osbuild/util/mnt.py
@@ -57,7 +57,16 @@ class MountGuard(contextlib.AbstractContextManager):
         if options:
             args += ["-o", ",".join(options)]
 
-        subprocess.run(["mount"] + args + [source, target], check=True)
+        r = subprocess.run(["mount"] + args + [source, target],
+                           stderr=subprocess.STDOUT,
+                           stdout=subprocess.PIPE,
+                           encoding="utf-8",
+                           check=False)
+        if r.returncode != 0:
+            code = r.returncode
+            msg = r.stdout.strip()
+            raise RuntimeError(f"{msg} (code: {code})")
+
         self.mounts += [{"source": source, "target": target}]
 
     def umount(self):
diff --git a/test/mod/test_util_mnt.py b/test/mod/test_util_mnt.py
new file mode 100644
index 00000000..ad225016
--- /dev/null
+++ b/test/mod/test_util_mnt.py
@@ -0,0 +1,22 @@
+import os
+import subprocess
+
+import pytest
+
+from osbuild.util.mnt import mount, MountGuard
+
+
+@pytest.mark.skipif(os.getuid() != 0, reason="root only")
+def test_mount_failure_msg(tmp_path):
+    with pytest.raises(RuntimeError) as e:
+        mount("/dev/invalid-src", tmp_path)
+    assert "special device /dev/invalid-src does not exist" in str(e.value)
+
+
+@pytest.mark.skipif(os.getuid() != 0, reason="root only")
+def test_mount_guard_failure_msg(tmp_path):
+    with pytest.raises(RuntimeError) as e:
+        with MountGuard() as mg:
+            mg.mount("/dev/invalid-src", tmp_path)
+    assert "special device /dev/invalid-src does not exist" in str(e.value)
+