diff --git a/changelog.d/12177.bugfix b/changelog.d/12177.bugfix
new file mode 100644
index 0000000000000000000000000000000000000000..3f2852f345b945ccef6da249234633a4bba49ea8
--- /dev/null
+++ b/changelog.d/12177.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in 1.54.0rc1 which meant that Synapse would refuse to start if pre-release versions of dependencies were installed.
\ No newline at end of file
diff --git a/synapse/util/check_dependencies.py b/synapse/util/check_dependencies.py
index 39b0a91db3e82d6cdb517e375604efded031ccfc..12cd8049392fd2b3e70f20d175cab498ecc079ae 100644
--- a/synapse/util/check_dependencies.py
+++ b/synapse/util/check_dependencies.py
@@ -163,7 +163,8 @@ def check_requirements(extra: Optional[str] = None) -> None:
                 deps_unfulfilled.append(requirement.name)
                 errors.append(_not_installed(requirement, extra))
         else:
-            if not requirement.specifier.contains(dist.version):
+            # We specify prereleases=True to allow prereleases such as RCs.
+            if not requirement.specifier.contains(dist.version, prereleases=True):
                 deps_unfulfilled.append(requirement.name)
                 errors.append(_incorrect_version(requirement, dist.version, extra))
 
diff --git a/tests/util/test_check_dependencies.py b/tests/util/test_check_dependencies.py
index a91c33272f369f8dec7e1348c9c36ed090f6f646..38e9f58ac6cab9a439c4984b74b0b8c5e565e708 100644
--- a/tests/util/test_check_dependencies.py
+++ b/tests/util/test_check_dependencies.py
@@ -27,7 +27,9 @@ class DummyDistribution(metadata.Distribution):
 
 
 old = DummyDistribution("0.1.2")
+old_release_candidate = DummyDistribution("0.1.2rc3")
 new = DummyDistribution("1.2.3")
+new_release_candidate = DummyDistribution("1.2.3rc4")
 
 # could probably use stdlib TestCase --- no need for twisted here
 
@@ -110,3 +112,20 @@ class TestDependencyChecker(TestCase):
             with self.mock_installed_package(new):
                 # should not raise
                 check_requirements("cool-extra")
+
+    def test_release_candidates_satisfy_dependency(self) -> None:
+        """
+        Tests that release candidates count as far as satisfying a dependency
+        is concerned.
+        (Regression test, see #12176.)
+        """
+        with patch(
+            "synapse.util.check_dependencies.metadata.requires",
+            return_value=["dummypkg >= 1"],
+        ):
+            with self.mock_installed_package(old_release_candidate):
+                self.assertRaises(DependencyException, check_requirements)
+
+            with self.mock_installed_package(new_release_candidate):
+                # should not raise
+                check_requirements()