diff --git a/changelog.d/3892.bugfix b/changelog.d/3892.bugfix
new file mode 100644
index 0000000000..8b30afab04
--- /dev/null
+++ b/changelog.d/3892.bugfix
@@ -0,0 +1 @@
+Fix some b'abcd' noise in logs and metrics
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index 13b19f7626..083484a687 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -244,7 +244,10 @@ class MatrixFederationHttpClient(object):
                             request_deferred,
                         )
 
-                    log_result = "%d %s" % (response.code, response.phrase,)
+                    log_result = "%d %s" % (
+                        response.code,
+                        response.phrase.decode('ascii', errors='replace'),
+                    )
                     break
                 except Exception as e:
                     if not retry_on_dns_fail and isinstance(e, DNSLookupError):
diff --git a/synapse/http/site.py b/synapse/http/site.py
index e1e53e8ae5..2191de9836 100644
--- a/synapse/http/site.py
+++ b/synapse/http/site.py
@@ -82,7 +82,7 @@ class SynapseRequest(Request):
         )
 
     def get_request_id(self):
-        return "%s-%i" % (self.method, self.request_seq)
+        return "%s-%i" % (self.method.decode('ascii'), self.request_seq)
 
     def get_redacted_uri(self):
         uri = self.uri
@@ -119,7 +119,7 @@ class SynapseRequest(Request):
             # dispatching to the handler, so that the handler
             # can update the servlet name in the request
             # metrics
-            requests_counter.labels(self.method,
+            requests_counter.labels(self.method.decode('ascii'),
                                     self.request_metrics.name).inc()
 
     @contextlib.contextmanager
@@ -280,9 +280,9 @@ class SynapseRequest(Request):
             int(usage.db_txn_count),
             self.sentLength,
             code,
-            self.method,
+            self.method.decode('ascii'),
             self.get_redacted_uri(),
-            self.clientproto,
+            self.clientproto.decode('ascii', errors='replace'),
             user_agent,
             usage.evt_db_fetch_count,
         )