diff --git a/.hlint.yaml b/.hlint.yaml
index 95735a3ca8..3aac4d9b13 100644
--- a/.hlint.yaml
+++ b/.hlint.yaml
@@ -16,6 +16,7 @@
 # custom rules:
 - hint: { lhs: (() <$), rhs: void }
 - hint: { lhs: return, rhs: pure }
+- hint: { lhs:  maybe mempty, rhs: foldMap }
 
 # We want the latter function because it handles signals properly.
 - error: { name: Use shutdown, lhs: runSettings, rhs: runSettingsWithShutdown }
diff --git a/libs/wire-api/src/Wire/API/Call/Config.hs b/libs/wire-api/src/Wire/API/Call/Config.hs
index 3777bdcbb7..4c45d67875 100644
--- a/libs/wire-api/src/Wire/API/Call/Config.hs
+++ b/libs/wire-api/src/Wire/API/Call/Config.hs
@@ -255,7 +255,7 @@ instance BC.ToByteString TurnURI where
       <> BC.builder h
       <> byteString ":"
       <> BC.builder p
-      <> maybe mempty ((byteString "?transport=" <>) . BC.builder) tp
+      <> foldMap ((byteString "?transport=" <>) . BC.builder) tp
 
 instance BC.FromByteString TurnURI where
   parser = BC.parser >>= either fail pure . parseTurnURI
diff --git a/libs/wire-api/src/Wire/API/User/Profile.hs b/libs/wire-api/src/Wire/API/User/Profile.hs
index 37b3557e31..f634fe7f08 100644
--- a/libs/wire-api/src/Wire/API/User/Profile.hs
+++ b/libs/wire-api/src/Wire/API/User/Profile.hs
@@ -185,7 +185,7 @@ instance Show Locale where
   show = Text.unpack . locToText
 
 locToText :: Locale -> Text
-locToText (Locale l c) = lan2Text l <> maybe mempty (("-" <>) . con2Text) c
+locToText (Locale l c) = lan2Text l <> foldMap (("-" <>) . con2Text) c
 
 parseLocale :: Text -> Maybe Locale
 parseLocale = hush . parseOnly localeParser
diff --git a/libs/zauth/src/Data/ZAuth/Token.hs b/libs/zauth/src/Data/ZAuth/Token.hs
index a4319822dc..50966b5310 100644
--- a/libs/zauth/src/Data/ZAuth/Token.hs
+++ b/libs/zauth/src/Data/ZAuth/Token.hs
@@ -339,7 +339,7 @@ writeHeader t =
     <> dot
     <> field "t" (t ^. typ)
     <> dot
-    <> field "l" (maybe mempty builder (t ^. tag))
+    <> field "l" (foldMap builder (t ^. tag))
 
 instance ToByteString Access where
   builder t =
diff --git a/services/galley/src/Galley/API/Update.hs b/services/galley/src/Galley/API/Update.hs
index 27b2d6c806..b085feabb3 100644
--- a/services/galley/src/Galley/API/Update.hs
+++ b/services/galley/src/Galley/API/Update.hs
@@ -1269,7 +1269,7 @@ unqualifyEndpoint loc f ignoreMissing reportMissing message = do
             qualifiedNewOtrNativePush = newOtrNativePush message,
             qualifiedNewOtrTransient = newOtrTransient message,
             qualifiedNewOtrNativePriority = newOtrNativePriority message,
-            qualifiedNewOtrData = maybe mempty fromBase64TextLenient (newOtrData message),
+            qualifiedNewOtrData = foldMap fromBase64TextLenient (newOtrData message),
             qualifiedNewOtrClientMismatchStrategy = clientMismatchStrategy
           }
   unqualify (tDomain loc) <$> f qualifiedMessage
diff --git a/services/galley/src/Galley/Intra/Spar.hs b/services/galley/src/Galley/Intra/Spar.hs
index e9429ca244..7d005d8585 100644
--- a/services/galley/src/Galley/Intra/Spar.hs
+++ b/services/galley/src/Galley/Intra/Spar.hs
@@ -47,4 +47,4 @@ lookupScimUserInfos uids = do
       method POST
         . paths ["i", "scim", "userinfos"]
         . json (UserSet $ Set.fromList uids)
-  pure $ maybe mempty scimUserInfos $ responseJsonMaybe response
+  pure $ foldMap scimUserInfos $ responseJsonMaybe response
diff --git a/services/gundeck/test/unit/Native.hs b/services/gundeck/test/unit/Native.hs
index 27fee4380d..0d99b69600 100644
--- a/services/gundeck/test/unit/Native.hs
+++ b/services/gundeck/test/unit/Native.hs
@@ -79,10 +79,10 @@ instance FromJSON SnsNotification where
     where
       parseApns t n =
         let apn = decodeStrict' (T.encodeUtf8 n)
-         in maybe mempty (pure . SnsNotification t . SnsApnsData) apn
+         in foldMap (pure . SnsNotification t . SnsApnsData) apn
       parseGcm n =
         let gcm = decodeStrict' (T.encodeUtf8 n)
-         in maybe mempty (pure . SnsNotification GCM . SnsGcmData) gcm
+         in foldMap (pure . SnsNotification GCM . SnsGcmData) gcm
 
 data SnsData
   = SnsGcmData !GcmData
diff --git a/services/spar/test-integration/Test/MetricsSpec.hs b/services/spar/test-integration/Test/MetricsSpec.hs
index ab6a87136b..32f2d845d1 100644
--- a/services/spar/test-integration/Test/MetricsSpec.hs
+++ b/services/spar/test-integration/Test/MetricsSpec.hs
@@ -37,7 +37,7 @@ spec = describe "metrics" . it "works" $ do
   _ <- call $ get (spar . path p1)
   _ <- call $ get (spar . path (p2 "316f1c18-2980-11e9-ab0b-ef604d1791b2"))
   _ <- call $ get (spar . path (p2 "60a7dda8-2980-11e9-b359-fb5b41565453"))
-  resp :: String <- call $ maybe mempty cs . responseBody <$> get (spar . path "i/metrics")
+  resp :: String <- call $ foldMap cs . responseBody <$> get (spar . path "i/metrics")
   -- FUTUREWORK: here we could parse the prometheus 'RegistrySample' and inspect it more
   -- thoroughly, but i'm not sure there is a parser.
   liftIO $ do