diff --git a/src/PostgREST/DbStructure.hs b/src/PostgREST/DbStructure.hs
index 8e0230bde..81a528757 100644
--- a/src/PostgREST/DbStructure.hs
+++ b/src/PostgREST/DbStructure.hs
@@ -19,7 +19,7 @@ import qualified Data.HashMap.Strict           as M
 import           Data.List                     (elemIndex)
 import           Data.Maybe                    (fromJust)
 import           Data.Text                     (split, strip,
-                                                breakOn, dropAround)
+                                                breakOn, dropAround, splitOn)
 import qualified Data.Text                     as T
 import qualified Hasql.Session                 as H
 import           PostgREST.Types
@@ -120,11 +120,12 @@ decodeProcs =
     addName pd = (pdName pd, pd)
 
     parseArgs :: Text -> [PgArg]
-    parseArgs = mapMaybe (parseArg . strip) . split (==',')
+    parseArgs = mapMaybe parseArg . filter (not . isPrefixOf "OUT" . toS) . map strip . split (==',')
 
     parseArg :: Text -> Maybe PgArg
     parseArg a =
-      let (body, def) = breakOn " DEFAULT " a
+      let arg = lastDef "" $ splitOn "INOUT " a
+          (body, def) = breakOn " DEFAULT " arg
           (name, typ) = breakOn " " body in
       if T.null typ
          then Nothing
diff --git a/test/Feature/StructureSpec.hs b/test/Feature/StructureSpec.hs
index c6b52c55e..26ab0ef9f 100644
--- a/test/Feature/StructureSpec.hs
+++ b/test/Feature/StructureSpec.hs
@@ -200,6 +200,22 @@ spec = do
 
         liftIO $ funcTag `shouldBe` Just [aesonQQ|"(rpc) privileged_hello"|]
 
+      it "doesn't include OUT params of function as required parameters" $ do
+        r <- simpleBody <$> get "/"
+        let params = r ^? key "paths" . key "/rpc/many_out_params"
+                        . key "post" . key "parameters" .  nth 0
+                        . key "schema". key "required"
+
+        liftIO $ params `shouldBe` Nothing
+
+      it "includes INOUT params(with no DEFAULT) of function as required parameters" $ do
+        r <- simpleBody <$> get "/"
+        let params = r ^? key "paths" . key "/rpc/many_inout_params"
+                        . key "post" . key "parameters" .  nth 0
+                        . key "schema". key "required"
+
+        liftIO $ params `shouldBe` Just [aesonQQ|["num", "str"]|]
+
   describe "Allow header" $ do
 
     it "includes read/write verbs for writeable table" $ do
diff --git a/test/fixtures/schema.sql b/test/fixtures/schema.sql
index b47f5c333..a9a76f9ac 100755
--- a/test/fixtures/schema.sql
+++ b/test/fixtures/schema.sql
@@ -1272,6 +1272,14 @@ create table test.being_part (
   being int not null references test.being(being),
   part int not null references test.part(part)
 );
+
+create function test.many_out_params(OUT my_json pg_catalog.json, OUT num int, OUT str text) AS $$
+  select '{"a": 1, "b": "two"}'::json, 3, 'four'::text;
+$$ language sql;
+
+create function test.many_inout_params(INOUT num int, INOUT str text, INOUT b bool DEFAULT true) AS $$
+  select num, str, b;
+$$ language sql;
 --
 -- PostgreSQL database dump complete
 --