diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 9021d4d57..87d0a4580 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -308,7 +308,7 @@ class RegistrationHandler(BaseHandler):
             logger.info("got threepid with medium '%s' and address '%s'",
                         threepid['medium'], threepid['address'])
 
-            if not check_3pid_allowed(self.hs, threepid['medium'], threepid['address']):
+            if not (yield check_3pid_allowed(self.hs, threepid['medium'], threepid['address'])):
                 raise RegistrationError(
                     403, "Third party identifier is not allowed"
                 )
diff --git a/synapse/rest/client/v2_alpha/account.py b/synapse/rest/client/v2_alpha/account.py
index 30523995a..7d43a3361 100644
--- a/synapse/rest/client/v2_alpha/account.py
+++ b/synapse/rest/client/v2_alpha/account.py
@@ -48,7 +48,7 @@ class EmailPasswordRequestTokenRestServlet(RestServlet):
             'id_server', 'client_secret', 'email', 'send_attempt'
         ])
 
-        if not check_3pid_allowed(self.hs, "email", body['email']):
+        if not (yield check_3pid_allowed(self.hs, "email", body['email'])):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
@@ -84,7 +84,7 @@ class MsisdnPasswordRequestTokenRestServlet(RestServlet):
 
         msisdn = phone_number_to_msisdn(body['country'], body['phone_number'])
 
-        if not check_3pid_allowed(self.hs, "msisdn", msisdn):
+        if not (yield check_3pid_allowed(self.hs, "msisdn", msisdn)):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
@@ -228,7 +228,7 @@ class EmailThreepidRequestTokenRestServlet(RestServlet):
         if absent:
             raise SynapseError(400, "Missing params: %r" % absent, Codes.MISSING_PARAM)
 
-        if not check_3pid_allowed(self.hs, "email", body['email']):
+        if not (yield check_3pid_allowed(self.hs, "email", body['email'])):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
@@ -271,7 +271,7 @@ class MsisdnThreepidRequestTokenRestServlet(RestServlet):
 
         msisdn = phone_number_to_msisdn(body['country'], body['phone_number'])
 
-        if not check_3pid_allowed(self.hs, "msisdn", msisdn):
+        if not (yield check_3pid_allowed(self.hs, "msisdn", msisdn)):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index c6f4680a7..7824456eb 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -71,7 +71,7 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
             'id_server', 'client_secret', 'email', 'send_attempt'
         ])
 
-        if not check_3pid_allowed(self.hs, "email", body['email']):
+        if not (yield check_3pid_allowed(self.hs, "email", body['email'])):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
@@ -111,7 +111,7 @@ class MsisdnRegisterRequestTokenRestServlet(RestServlet):
 
         msisdn = phone_number_to_msisdn(body['country'], body['phone_number'])
 
-        if not check_3pid_allowed(self.hs, "msisdn", msisdn):
+        if not (yield check_3pid_allowed(self.hs, "msisdn", msisdn)):
             raise SynapseError(
                 403, "Third party identifier is not allowed", Codes.THREEPID_DENIED,
             )
@@ -371,7 +371,7 @@ class RegisterRestServlet(RestServlet):
                     medium = auth_result[login_type]['medium']
                     address = auth_result[login_type]['address']
 
-                    if not check_3pid_allowed(self.hs, medium, address):
+                    if not (yield check_3pid_allowed(self.hs, medium, address)):
                         raise SynapseError(
                             403, "Third party identifier is not allowed",
                             Codes.THREEPID_DENIED,