diff --git a/CHANGELOG.md b/CHANGELOG.md
index a8248ca7b..f3647e2c8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - #1242, Fix embedding a view having a select in a where - @steve-chavez
 - #1238, Fix PostgreSQL to OpenAPI type mappings for numeric and character types - @fpusch
 - #1265, Fix query generated on bulk upsert with an empty array - @qu4tro
+- #1273, Fix RPC ignoring unknown arguments by default - @steve-chavez
 
 ## [5.2.0] - 2018-12-12
 
diff --git a/src/PostgREST/App.hs b/src/PostgREST/App.hs
index ce42322fe..b8427585d 100644
--- a/src/PostgREST/App.hs
+++ b/src/PostgREST/App.hs
@@ -282,9 +282,8 @@ app dbStructure proc cols conf apiRequest =
             Left errorResponse -> return errorResponse
             Right ((q, cq), bField) -> do
               let singular = contentType == CTSingularJSON
-                  specifiedPgArgs = filter ((`S.member` cols) . pgaName) $ maybe [] pdArgs proc
               row <- H.statement (toS $ pjRaw pJson) $
-                callProc qi specifiedPgArgs returnsScalar q cq shouldCount
+                callProc qi (specifiedProcArgs cols proc) returnsScalar q cq shouldCount
                          singular (iPreferSingleObjectParameter apiRequest)
                          (contentType == CTTextCSV)
                          (contentType == CTOctetStream) bField
diff --git a/src/PostgREST/Types.hs b/src/PostgREST/Types.hs
index fa4ccd205..a9a24033a 100644
--- a/src/PostgREST/Types.hs
+++ b/src/PostgREST/Types.hs
@@ -111,6 +111,17 @@ findProc qi payloadKeys paramsAsSingleObject allProcs =
              else payloadKeys `S.isSubsetOf` S.fromList (pgaName <$> pdArgs x))
   ) <$> procs
 
+{-|
+  Search the procedure parameters by matching them with the specified keys.
+  If the key doesn't match a parameter, a parameter with a default type "text" is assumed.
+-}
+specifiedProcArgs :: S.Set FieldName -> Maybe ProcDescription -> [PgArg]
+specifiedProcArgs keys proc =
+  let
+    args = maybe [] pdArgs proc
+  in
+  (\k -> fromMaybe (PgArg k "text" True) (find ((==) k . pgaName) args)) <$> S.toList keys
+
 type Schema = Text
 type TableName = Text
 type SqlQuery = Text
@@ -378,7 +389,10 @@ instance Ord PgVersion where
 
 -- | Tells the minimum PostgreSQL version required by this version of PostgREST
 minimumPgVersion :: PgVersion
-minimumPgVersion = PgVersion 90400 "9.4"
+minimumPgVersion = pgVersion94
+
+pgVersion94 :: PgVersion
+pgVersion94 = PgVersion 90400 "9.4"
 
 pgVersion95 :: PgVersion
 pgVersion95 = PgVersion 90500 "9.5"
diff --git a/test/Feature/RpcSpec.hs b/test/Feature/RpcSpec.hs
index c3752b660..00d06a114 100644
--- a/test/Feature/RpcSpec.hs
+++ b/test/Feature/RpcSpec.hs
@@ -13,8 +13,10 @@ import Network.Wai (Application)
 
 import Protolude hiding (get)
 
-spec :: SpecWith Application
-spec =
+import PostgREST.Types (PgVersion, pgVersion95)
+
+spec :: PgVersion -> SpecWith Application
+spec actualPgVersion =
   describe "remote procedure call" $ do
     context "a proc that returns a set" $ do
       it "returns paginated results" $ do
@@ -77,6 +79,21 @@ spec =
       it "should fail with 404 on unknown proc args" $ do
         get "/rpc/sayhello" `shouldRespondWith` 404
         get "/rpc/sayhello?any_arg=value" `shouldRespondWith` 404
+      it "should not ignore unknown args and fail with 404" $
+        get "/rpc/add_them?a=1&b=2&smthelse=blabla" `shouldRespondWith`
+        let
+          message :: Text
+          message
+            | actualPgVersion < pgVersion95 = "function test.add_them(a := integer, b := integer, smthelse := text) does not exist"
+            | otherwise = "function test.add_them(a => integer, b => integer, smthelse => text) does not exist"
+        in [json| {
+          "code": "42883",
+          "details": null,
+          "hint": "No function matches the given name and argument types. You might need to add explicit type casts.",
+          "message": #{message} } |]
+        { matchStatus  = 404
+        , matchHeaders = [matchContentTypeJson]
+        }
 
     it "works when having uppercase identifiers" $ do
       get "/rpc/quotedFunction?user=mscott&fullName=Michael Scott&SSN=401-32-XXXX" `shouldRespondWith`
diff --git a/test/Main.hs b/test/Main.hs
index 8f9a6797b..897bdf38d 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -87,7 +87,7 @@ main = do
         , ("Feature.InsertSpec"             , Feature.InsertSpec.spec actualPgVersion)
         , ("Feature.JsonOperatorSpec"       , Feature.JsonOperatorSpec.spec actualPgVersion)
         , ("Feature.QuerySpec"              , Feature.QuerySpec.spec)
-        , ("Feature.RpcSpec"                , Feature.RpcSpec.spec)
+        , ("Feature.RpcSpec"                , Feature.RpcSpec.spec actualPgVersion)
         , ("Feature.RangeSpec"              , Feature.RangeSpec.spec)
         , ("Feature.SingularSpec"           , Feature.SingularSpec.spec)
         , ("Feature.StructureSpec"          , Feature.StructureSpec.spec)