diff --git a/synapse/config/_base.py b/synapse/config/_base.py

index 5613f38e4d..a219a83550 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -405,7 +405,10 @@ class Config(object):
             self.invoke_all("generate_files", config)
             return
 
-        self.invoke_all("read_config", config)
+        self.parse_config_dict(config)
+
+    def parse_config_dict(self, config_dict):
+        self.invoke_all("read_config", config_dict)
 
 
 def find_config_files(search_paths):
diff --git a/synapse/config/key.py b/synapse/config/key.py

index 2bd5531acb..933928885a 100644
--- a/synapse/config/key.py
+++ b/synapse/config/key.py
@@ -38,7 +38,12 @@ logger = logging.getLogger(__name__)
 class KeyConfig(Config):
 
     def read_config(self, config):
-        self.signing_key = self.read_signing_key(config["signing_key_path"])
+        # the signing key can be specified inline or in a separate file
+        if "signing_key" in config:
+            self.signing_key = read_signing_keys([config["signing_key"]])
+        else:
+            self.signing_key = self.read_signing_key(config["signing_key_path"])
+
         self.old_signing_keys = self.read_old_signing_keys(
             config.get("old_signing_keys", {})
         )