diff --git a/actions/arch-package/arch-package.sh b/actions/arch-package/arch-package.sh
--- a/actions/arch-package/arch-package.sh
+++ b/actions/arch-package/arch-package.sh
@@ -71,7 +71,8 @@ fi
 
 # Detect application name and version
 tar_basename="$(basename "$tarball" .tar.gz)"
-if [[ "$tar_basename" =~ ^([a-zA-Z0-9_-]+)-([0-9]+\.[0-9]+\.[0-9]+[^-_]*)-linux-([a-zA-Z0-9_]+)$ ]]; then
+# The version may carry a prerelease (1.2.3-rc.1): the hyphens are dropped from pkgver below.
+if [[ "$tar_basename" =~ ^([a-zA-Z0-9_-]+)-([0-9]+\.[0-9]+\.[0-9]+[^_]*)-linux-([a-zA-Z0-9_]+)$ ]]; then
   app="${BASH_REMATCH[1]}"
   raw_version="${BASH_REMATCH[2]}"
 else
@@ -91,15 +92,14 @@ if [[ ! "$app" =~ ^[a-zA-Z0-9][a-zA-Z0-9_+.-]*$ ]]; then
   die "invalid application name derived from archive: '$app'"
 fi
 
-# Format Arch pkgver (no hyphens or tildes allowed in pkgver)
-upstream="${raw_version%-*}"
-if [[ "$upstream" != "$raw_version" ]]; then
-  rel="${raw_version##*-}"
-  if [[ "$rel" =~ ^[0-9]+$ ]]; then
-    pkgrel="$rel"
-  fi
+# Format Arch pkgver (no hyphens or tildes allowed in pkgver). The version is semver, so a
+# hyphen starts a prerelease, not a package release; joined on, it still sorts before the
+# release in pacman (1.2.3rc.1 < 1.2.3).
+pkgver="${raw_version//\~/}"
+# A numeric prerelease needs a letter in front: 1.2.3-1 as 1.2.31 would sort after 1.2.4.
+if [[ "$pkgver" =~ ^[0-9]+\.[0-9]+\.[0-9]+-+[0-9] ]]; then
+  pkgver="${pkgver/-/pre}"
 fi
-pkgver="${upstream//\~/}"
 pkgver="${pkgver//-/}"
 # pkgver, pkgrel and the license words are written into PKGBUILD, which makepkg sources as
 # Bash; the tarball name and the environment are not trusted to be shell-safe.
diff --git a/tests/test_arch.py b/tests/test_arch.py
--- a/tests/test_arch.py
+++ b/tests/test_arch.py
@@ -210,6 +210,33 @@ exit 0
             )
             self.assertIn("provides=(myapp=1.2.3-2)", pkgbuild)
 
+    def test_prerelease_version_from_the_tarball_name(self):
+        # release.yml names the tarball after the resolved version, so a prerelease such as a
+        # 0.2.0-rc.1 test run reaches here with a hyphen in it. Arch pkgver has no hyphens; each
+        # form below still sorts before its release in pacman.
+        for version, pkgver in (("0.2.0-rc.1", "0.2.0rc.1"), ("1.2.3-1", "1.2.3pre1"), ("1.2.3--1", "1.2.3pre1")):
+            with self.subTest(version=version), tempfile.TemporaryDirectory() as tmpdir:
+                tmp_path = Path(tmpdir)
+                tarball = self._create_fixture_tarball(tmp_path, filename=f"myapp-{version}-linux-x86_64.tar.gz")
+                tools = self._setup_mock_tools(tmp_path)
+                # Extract for real: an unmatched name falls back to the archive's executable.
+                (tools / "tar").unlink()
+                capture = tmp_path / "capture"
+                capture.mkdir()
+                res = subprocess.run(
+                    [str(ARCH_SCRIPT), str(tarball), "x86_64", str(tmp_path / "out")],
+                    capture_output=True,
+                    text=True,
+                    env={**os.environ, "PATH": f"{tools}:{os.environ['PATH']}", "MOCK_CAPTURE": str(capture)},
+                )
+                self.assertEqual(res.returncode, 0, f"{res.stderr}\n{res.stdout}")
+                pkgbuild = (capture / "PKGBUILD").read_text()
+                self.assertIn(f"pkgver={pkgver}\n", pkgbuild)
+                self.assertIn("pkgrel=1\n", pkgbuild)
+                self.assertIn(f"provides=(myapp={pkgver}-1)", pkgbuild)
+                self.assertEqual([p.name for p in (tmp_path / "out").iterdir()],
+                                 [f"myapp-{version}-linux-x86_64.pkg.tar.zst"])
+
     def test_package_function_rejects_symlinked_license_dir(self):
         with tempfile.TemporaryDirectory() as tmpdir:
             tmp_path = Path(tmpdir)