diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index 5f94c3181..88d09d9ba 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -99,7 +99,8 @@ class EventFederationStore(SQLBaseStore):
                     "event_id": event_id,
                     "prev_event_id": e_id,
                     "room_id": room_id,
-                }
+                },
+                or_ignore=True,
             )
 
         # Update the extremities table if this is not an outlier.
@@ -120,7 +121,7 @@ class EventFederationStore(SQLBaseStore):
             # We only insert as a forward extremity the new pdu if there are no
             # other pdus that reference it as a prev pdu
             query = (
-                "INSERT INTO %(table)s (event_id, room_id) "
+                "INSERT OR IGNORE INTO %(table)s (event_id, room_id) "
                 "SELECT ?, ? WHERE NOT EXISTS ("
                 "SELECT 1 FROM %(event_edges)s WHERE "
                 "prev_event_id = ? "
@@ -144,7 +145,8 @@ class EventFederationStore(SQLBaseStore):
                     values={
                         "event_id": e_id,
                         "room_id": room_id,
-                    }
+                    },
+                    or_ignore=True,
                 )
 
             # Also delete from the backwards extremities table all ones that
diff --git a/synapse/storage/signatures.py b/synapse/storage/signatures.py
index b8f8fd44c..5e99174fc 100644
--- a/synapse/storage/signatures.py
+++ b/synapse/storage/signatures.py
@@ -181,11 +181,16 @@ class SignatureStore(SQLBaseStore):
             algorithm (str): Hashing algorithm.
             hash_bytes (bytes): Hash function output bytes.
         """
-        self._simple_insert_txn(txn, "event_content_hashes", {
-            "event_id": event_id,
-            "algorithm": algorithm,
-            "hash": buffer(hash_bytes),
-        })
+        self._simple_insert_txn(
+            txn,
+            "event_content_hashes",
+            {
+                "event_id": event_id,
+                "algorithm": algorithm,
+                "hash": buffer(hash_bytes),
+            },
+            or_ignore=True,
+        )
 
     def _get_event_reference_hashes_txn(self, txn, event_id):
         """Get all the hashes for a given PDU.
@@ -212,11 +217,16 @@ class SignatureStore(SQLBaseStore):
             algorithm (str): Hashing algorithm.
             hash_bytes (bytes): Hash function output bytes.
         """
-        self._simple_insert_txn(txn, "event_reference_hashes", {
-            "event_id": event_id,
-            "algorithm": algorithm,
-            "hash": buffer(hash_bytes),
-        })
+        self._simple_insert_txn(
+            txn,
+            "event_reference_hashes",
+            {
+                "event_id": event_id,
+                "algorithm": algorithm,
+                "hash": buffer(hash_bytes),
+            },
+            or_ignore=True,
+        )
 
 
     def _get_event_origin_signatures_txn(self, txn, event_id):
@@ -245,12 +255,17 @@ class SignatureStore(SQLBaseStore):
             key_id (str): Id for the signing key.
             signature (bytes): The signature.
         """
-        self._simple_insert_txn(txn, "event_origin_signatures", {
-            "event_id": event_id,
-            "origin": origin,
-            "key_id": key_id,
-            "signature": buffer(signature_bytes),
-        })
+        self._simple_insert_txn(
+            txn,
+            "event_origin_signatures",
+            {
+                "event_id": event_id,
+                "origin": origin,
+                "key_id": key_id,
+                "signature": buffer(signature_bytes),
+            },
+            or_ignore=True,
+        )
 
     def _get_prev_event_hashes_txn(self, txn, event_id):
         """Get all the hashes for previous PDUs of a PDU
@@ -274,9 +289,14 @@ class SignatureStore(SQLBaseStore):
 
     def _store_prev_event_hash_txn(self, txn, event_id, prev_event_id,
                                  algorithm, hash_bytes):
-        self._simple_insert_txn(txn, "event_edge_hashes", {
-            "event_id": event_id,
-            "prev_event_id": prev_event_id,
-            "algorithm": algorithm,
-            "hash": buffer(hash_bytes),
-        })
\ No newline at end of file
+        self._simple_insert_txn(
+            txn,
+            "event_edge_hashes",
+            {
+                "event_id": event_id,
+                "prev_event_id": prev_event_id,
+                "algorithm": algorithm,
+                "hash": buffer(hash_bytes),
+            },
+            or_ignore=True,
+        )
\ No newline at end of file