diff --git a/pdfly/up2.py b/pdfly/up2.py
index 01b1c2a..ab902b0 100644
--- a/pdfly/up2.py
+++ b/pdfly/up2.py
@@ -18,7 +18,9 @@ def main(pdf: Path, output: Path) -> None:
     for i in range(0, len(reader.pages) - 1, 2):
         lhs = reader.pages[i]
         rhs = reader.pages[i + 1]
-        lhs.merge_translated_page(rhs, float(lhs.mediabox.right), 0, True)
+        lhs.merge_translated_page(
+            rhs, tx=float(lhs.mediabox.width), ty=0, expand=True
+        )
         writer.add_page(lhs)
         print(str(i) + " ")
         sys.stdout.flush()
diff --git a/resources/input8.pdf b/resources/input8.pdf
new file mode 100644
index 0000000..f11b56d
Binary files /dev/null and b/resources/input8.pdf differ
diff --git a/tests/test_up2.py b/tests/test_up2.py
new file mode 100644
index 0000000..c29467a
--- /dev/null
+++ b/tests/test_up2.py
@@ -0,0 +1,63 @@
+import os
+import pytest
+from pypdf import PdfReader
+
+from .conftest import RESOURCES_ROOT, chdir, run_cli
+
+
+def test_up2_fewer_args(capsys, tmp_path):
+    with chdir(tmp_path):
+        exit_code = run_cli(["2-up", str(RESOURCES_ROOT / "box.pdf")])
+    assert exit_code == 2
+    captured = capsys.readouterr()
+    assert "Missing argument" in captured.err
+
+
+def test_up2_extra_args(capsys, tmp_path):
+    with chdir(tmp_path):
+        exit_code = run_cli(
+            [
+                "2-up",
+                str(RESOURCES_ROOT / "box.pdf"),
+                "./out.pdf",
+                "./out2.pdf",
+            ]
+        )
+
+    assert exit_code == 2
+    captured = capsys.readouterr()
+    assert "unexpected extra argument" in captured.err
+
+    with chdir(tmp_path):
+        assert not os.path.exists("out.pdf"), f"'out.pdf' should not exist."
+        assert not os.path.exists("out2.pdf"), f"'out2.pdf' should not exist."
+
+
+def test_up2_8page_file(capsys, tmp_path):
+    # Act
+    with chdir(tmp_path):
+        exit_code = run_cli(
+            [
+                "2-up",
+                str(RESOURCES_ROOT / "input8.pdf"),
+                "./out.pdf",
+            ]
+        )
+    captured = capsys.readouterr()
+
+    # Assert
+    assert exit_code == 0, captured
+    assert not captured.err
+    in_reader = PdfReader(RESOURCES_ROOT / "input8.pdf")
+    out_reader = PdfReader(tmp_path / "./out.pdf")
+
+    assert len(in_reader.pages) == 8
+    assert len(out_reader.pages) == 4
+
+    in_width = in_reader.pages[0].mediabox.width
+    in_height = in_reader.pages[0].mediabox.height
+    out_width = out_reader.pages[0].mediabox.width
+    out_height = out_reader.pages[0].mediabox.height
+
+    assert out_width == 2 * in_width  # PR #78
+    assert out_height == out_height