diff --git a/changelog.d/6849.bugfix b/changelog.d/6849.bugfix
new file mode 100644
index 0000000000000000000000000000000000000000..d928a26ec682409547b3427440d2ad5adef08d6b
--- /dev/null
+++ b/changelog.d/6849.bugfix
@@ -0,0 +1 @@
+Fix Synapse refusing to start if `federation_certificate_verification_whitelist` option is blank.
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index 2e9e478a2ac79ef575f30c00c42b679e5c5954a2..2514b0713d4914d4a5870910e7c71ef2b0ac8906 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -109,6 +109,8 @@ class TlsConfig(Config):
         fed_whitelist_entries = config.get(
             "federation_certificate_verification_whitelist", []
         )
+        if fed_whitelist_entries is None:
+            fed_whitelist_entries = []
 
         # Support globs (*) in whitelist values
         self.federation_certificate_verification_whitelist = []  # type: List[str]