diff --git a/changelog.d/9123.misc b/changelog.d/9123.misc
new file mode 100644
index 000000000000..329600c40c2b
--- /dev/null
+++ b/changelog.d/9123.misc
@@ -0,0 +1 @@
+Add experimental support for running Synapse with PyPy.
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index bfd46a3730db..8a2b73b75e3c 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -86,8 +86,12 @@
 
 CONDITIONAL_REQUIREMENTS = {
     "matrix-synapse-ldap3": ["matrix-synapse-ldap3>=0.1"],
-    # we use execute_values with the fetch param, which arrived in psycopg 2.8.
-    "postgres": ["psycopg2>=2.8"],
+    "postgres": [
+        # we use execute_values with the fetch param, which arrived in psycopg 2.8.
+        "psycopg2>=2.8 ; platform_python_implementation != 'PyPy'",
+        "psycopg2cffi>=2.8 ; platform_python_implementation == 'PyPy'",
+        "psycopg2cffi-compat==1.1 ; platform_python_implementation == 'PyPy'",
+    ],
     # ACME support is required to provision TLS certificates from authorities
     # that use the protocol, such as Let's Encrypt.
     "acme": [
diff --git a/synapse/storage/engines/__init__.py b/synapse/storage/engines/__init__.py
index 035f9ea6e98b..d15ccfacdeb7 100644
--- a/synapse/storage/engines/__init__.py
+++ b/synapse/storage/engines/__init__.py
@@ -12,7 +12,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import platform
 
 from ._base import BaseDatabaseEngine, IncorrectDatabaseSetup
 from .postgres import PostgresEngine
@@ -28,11 +27,8 @@ def create_engine(database_config) -> BaseDatabaseEngine:
         return Sqlite3Engine(sqlite3, database_config)
 
     if name == "psycopg2":
-        # pypy requires psycopg2cffi rather than psycopg2
-        if platform.python_implementation() == "PyPy":
-            import psycopg2cffi as psycopg2  # type: ignore
-        else:
-            import psycopg2  # type: ignore
+        # Note that psycopg2cffi-compat provides the psycopg2 module on pypy.
+        import psycopg2  # type: ignore
 
         return PostgresEngine(psycopg2, database_config)
 
diff --git a/synapse/storage/engines/sqlite.py b/synapse/storage/engines/sqlite.py
index 5db0f0b520db..b3d1834efbec 100644
--- a/synapse/storage/engines/sqlite.py
+++ b/synapse/storage/engines/sqlite.py
@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import platform
 import struct
 import threading
 import typing
@@ -30,6 +31,11 @@ def __init__(self, database_module, database_config):
         database = database_config.get("args", {}).get("database")
         self._is_in_memory = database in (None, ":memory:",)
 
+        if platform.python_implementation() == "PyPy":
+            # pypy's sqlite3 module doesn't handle bytearrays, convert them
+            # back to bytes.
+            database_module.register_adapter(bytearray, lambda array: bytes(array))
+
         # The current max state_group, or None if we haven't looked
         # in the DB yet.
         self._current_state_group_id = None