diff --git a/docs/openapi.json b/docs/openapi.json
index 346559624..d7f16e69f 100644
--- a/docs/openapi.json
+++ b/docs/openapi.json
@@ -16311,6 +16311,14 @@
                     },
                     "ssl_mode": {
                         "type": "string",
+                        "enum": [
+                            "disable",
+                            "allow",
+                            "prefer",
+                            "require",
+                            "verify-ca",
+                            "verify-full"
+                        ],
                         "title": "SSL mode",
                         "description": "SSL mode",
                         "default": "prefer"
diff --git a/src/constants.py b/src/constants.py
index 88dd2aee5..81556042c 100644
--- a/src/constants.py
+++ b/src/constants.py
@@ -1,6 +1,6 @@
 """Constants used in business logic."""
 
-from typing import Final
+from typing import Final, Literal
 
 # Use Final[type] as type hint for all constants to ensure that type checkers (Mypy etc.)
 # will be able to detect assignements to such constants.
@@ -158,7 +158,7 @@
 
 # PostgreSQL connection constants
 # See: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNECT-SSLMODE
-POSTGRES_DEFAULT_SSL_MODE: Final[str] = "prefer"
+POSTGRES_DEFAULT_SSL_MODE: Final[Literal["prefer"]] = "prefer"
 # See: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNECT-GSSENCMODE
 POSTGRES_DEFAULT_GSS_ENCMODE: Final[str] = "prefer"
 
diff --git a/src/models/config.py b/src/models/config.py
index c245a4da3..c922be8de 100644
--- a/src/models/config.py
+++ b/src/models/config.py
@@ -228,8 +228,10 @@ class PostgreSQLDatabaseConfiguration(ConfigurationBase):
         description="Database namespace",
     )
 
-    ssl_mode: str = Field(
-        constants.POSTGRES_DEFAULT_SSL_MODE,
+    ssl_mode: Literal[
+        "disable", "allow", "prefer", "require", "verify-ca", "verify-full"
+    ] = Field(
+        default=constants.POSTGRES_DEFAULT_SSL_MODE,
         title="SSL mode",
         description="SSL mode",
     )
diff --git a/tests/unit/models/config/test_postgresql_database_configuration.py b/tests/unit/models/config/test_postgresql_database_configuration.py
index bddaf1ab3..5bff8c759 100644
--- a/tests/unit/models/config/test_postgresql_database_configuration.py
+++ b/tests/unit/models/config/test_postgresql_database_configuration.py
@@ -219,3 +219,48 @@ def test_postgresql_database_configuration_ca_cert_path(subtests: SubTests) -> N
                 port=1234,
                 ca_cert_path=Path(""),
             )  # pyright: ignore[reportCallIssue]
+
+
+def test_postgresql_database_configuration_ssl_mode(subtests: SubTests) -> None:
+    """Test the PostgreSQLDatabaseConfiguration model."""
+    ssl_modes = ("disable", "allow", "prefer", "require", "verify-ca", "verify-full")
+
+    for ssl_mode in ssl_modes:
+        with subtests.test(msg=f"SSL mode {ssl_mode}"):
+            # pylint: disable=no-member
+            c = PostgreSQLDatabaseConfiguration(
+                db="db",
+                user="user",
+                password="password",
+                ssl_mode=ssl_mode,
+            )  # pyright: ignore[reportCallIssue]
+
+            # most attributes are set to default values
+            assert c is not None
+            assert c.host == "localhost"
+            assert c.port == 5432
+            assert c.db == "db"
+            assert c.user == "user"
+            assert c.password.get_secret_value() == "password"
+            assert c.ssl_mode == ssl_mode
+            assert c.gss_encmode == POSTGRES_DEFAULT_GSS_ENCMODE
+            assert c.namespace == "public"
+            assert c.ca_cert_path is None
+
+
+def test_postgresql_database_configuration_improper_ssl_mode(
+    subtests: SubTests,
+) -> None:
+    """Test the PostgreSQLDatabaseConfiguration model."""
+    ssl_modes = ("foo", "bar", "baz", "")
+
+    for ssl_mode in ssl_modes:
+        with subtests.test(msg=f"SSL mode {ssl_mode}"):
+            with pytest.raises(ValueError, match="Input should be 'disable'"):
+                # pylint: disable=no-member
+                PostgreSQLDatabaseConfiguration(
+                    db="db",
+                    user="user",
+                    password="password",
+                    ssl_mode=ssl_mode,
+                )  # pyright: ignore[reportCallIssue]