diff --git a/CHANGELOG.md b/CHANGELOG.md
index de41d1c78..d7a44082e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - #1075, Allow filtering top-level resource based on embedded resources filters - @steve-chavez, @Iced-Sun
    + This is enabled by adding `!inner` to the embedded resource, e.g. `/projects?select=*,clients!inner(*)&clients.id=eq.12`
    + This behavior can be enabled by default with the `db-embed-default-join='inner'` config option, which saves the need for specifying `!inner` on every request. In this case, you can go back to the previous behavior per request by specifying `!left`  on the embedded resource, e.g `/projects?select=*,clients!left(*)&clients.id=eq.12`
+- #1988, Allow specifying `unknown` for the `is` operator - @steve-chavez
 
 ### Fixed
 
@@ -586,4 +587,4 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 - Make filter position match docs, e.g. `?order=col.asc` rather
-  than `?order=asc.col`.
\ No newline at end of file
+  than `?order=asc.col`.
diff --git a/src/PostgREST/Query/SqlFragment.hs b/src/PostgREST/Query/SqlFragment.hs
index f01744197..8007cc474 100644
--- a/src/PostgREST/Query/SqlFragment.hs
+++ b/src/PostgREST/Query/SqlFragment.hs
@@ -61,7 +61,8 @@ import PostgREST.Request.Types           (Alias, Field, Filter (..),
                                           Operation (..),
                                           OrderDirection (..),
                                           OrderNulls (..),
-                                          OrderTerm (..), SelectItem)
+                                          OrderTerm (..), SelectItem,
+                                          TrileanVal (..))
 
 import Protolude hiding (cast)
 
@@ -234,9 +235,18 @@ pgFmtFilter table (Filter fld (OpExpr hasNot oper)) = notOp <> " " <> case oper
    Op op val  -> pgFmtFieldOp op <> " " <> case op of
      "like"  -> unknownLiteral (T.map star val)
      "ilike" -> unknownLiteral (T.map star val)
-     "is"    -> isAllowed val
      _       -> unknownLiteral val
 
+   -- IS cannot be prepared. `PREPARE boolplan AS SELECT * FROM projects where id IS $1` will give a syntax error.
+   -- The above can be fixed by using `PREPARE boolplan AS SELECT * FROM projects where id IS NOT DISTINCT FROM $1;`
+   -- However that would not accept the TRUE/FALSE/NULL/UNKNOWN keywords. See: https://stackoverflow.com/questions/6133525/proper-way-to-set-preparedstatement-parameter-to-null-under-postgres.
+   -- This is why `IS` operands are whitelisted at the Parsers.hs level
+   Is triVal -> pgFmtField table fld <> " IS " <> case triVal of
+     TriTrue    -> "TRUE"
+     TriFalse   -> "FALSE"
+     TriNull    -> "NULL"
+     TriUnknown -> "UNKNOWN"
+
    -- We don't use "IN", we use "= ANY". IN has the following disadvantages:
    -- + No way to use an empty value on IN: "col IN ()" is invalid syntax. With ANY we can do "= ANY('{}')"
    -- + Can invalidate prepared statements: multiple parameters on an IN($1, $2, $3) will lead to using different prepared statements and not take advantage of caching.
@@ -252,13 +262,6 @@ pgFmtFilter table (Filter fld (OpExpr hasNot oper)) = notOp <> " " <> case oper
    sqlOperator o = SQL.sql $ M.lookupDefault "=" o operators
    notOp = if hasNot then "NOT" else mempty
    star c = if c == '*' then '%' else c
-   -- IS cannot be prepared. `PREPARE boolplan AS SELECT * FROM projects where id IS $1` will give a syntax error.
-   -- The above can be fixed by using `PREPARE boolplan AS SELECT * FROM projects where id IS NOT DISTINCT FROM $1;`
-   -- However that would not accept the TRUE/FALSE/NULL keywords. See: https://stackoverflow.com/questions/6133525/proper-way-to-set-preparedstatement-parameter-to-null-under-postgres.
-   isAllowed :: Text -> SQL.Snippet
-   isAllowed v = SQL.sql $ maybe
-     (pgFmtLit v <> "::unknown") encodeUtf8
-     (find ((==) . T.toLower $ v) ["null","true","false"])
 
 pgFmtJoinCondition :: JoinCondition -> SQL.Snippet
 pgFmtJoinCondition (JoinCondition (qi1, col1) (qi2, col2)) =
diff --git a/src/PostgREST/Request/Parsers.hs b/src/PostgREST/Request/Parsers.hs
index cd78e639e..4a8db797f 100644
--- a/src/PostgREST/Request/Parsers.hs
+++ b/src/PostgREST/Request/Parsers.hs
@@ -195,15 +195,22 @@ pOpExpr pSVal = try ( string "not" *> pDelimiter *> (OpExpr True <$> pOperation)
     pOperation =
           Op . toS <$> foldl1 (<|>) (try . ((<* pDelimiter) . string) . toS <$> M.keys ops) <*> pSVal
       <|> In <$> (try (string "in" *> pDelimiter) *> pListVal)
+      <|> Is <$> (try (string "is" *> pDelimiter) *> pTriVal)
       <|> pFts
       <?> "operator (eq, gt, ...)"
 
+    pTriVal = try (string "null"    $> TriNull)
+          <|> try (string "unknown" $> TriUnknown)
+          <|> try (string "true"    $> TriTrue)
+          <|> try (string "false"   $> TriFalse)
+          <?> "null or trilean value (unknown, true, false)"
+
     pFts = do
       op   <- foldl1 (<|>) (try . string . toS <$> ftsOps)
       lang <- optionMaybe $ try (between (char '(') (char ')') (many (letter <|> digit <|> oneOf "_")))
       pDelimiter >> Fts (toS op) (toS <$> lang) <$> pSVal
 
-    ops = M.filterWithKey (const . flip notElem ("in":ftsOps)) operators
+    ops = M.filterWithKey (const . flip notElem ("in":"is":ftsOps)) operators
     ftsOps = M.keys ftsOperators
 
 pSingleVal :: Parser SingleVal
diff --git a/src/PostgREST/Request/Types.hs b/src/PostgREST/Request/Types.hs
index 939d9b198..f33ba9a14 100644
--- a/src/PostgREST/Request/Types.hs
+++ b/src/PostgREST/Request/Types.hs
@@ -31,6 +31,7 @@ module PostgREST.Request.Types
   , ReadRequest
   , SelectItem
   , SingleVal
+  , TrileanVal(..)
   , fstFieldNames
   ) where
 
@@ -209,6 +210,7 @@ data OpExpr =
 data Operation
   = Op Operator SingleVal
   | In ListVal
+  | Is TrileanVal
   | Fts Operator (Maybe Language) SingleVal
   deriving (Eq)
 
@@ -220,3 +222,11 @@ type SingleVal = Text
 
 -- | Represents a list value in a filter, e.g. id=in.(val1,val2,val3)
 type ListVal = [Text]
+
+-- | Three-valued logic values
+data TrileanVal
+  = TriTrue
+  | TriFalse
+  | TriNull
+  | TriUnknown
+  deriving Eq
diff --git a/test/Feature/QuerySpec.hs b/test/Feature/QuerySpec.hs
index 52272ae02..5bfe6890f 100644
--- a/test/Feature/QuerySpec.hs
+++ b/test/Feature/QuerySpec.hs
@@ -73,6 +73,23 @@ spec actualPgVersion = do
 
       get "/nullable_integer?a=is.null" `shouldRespondWith` [json|[{"a":null}]|]
 
+    it "matches with trilean values" $ do
+      get "/chores?done=is.true" `shouldRespondWith`
+        [json| [{"id": 1, "name": "take out the garbage", "done": true }] |]
+        { matchHeaders = [matchContentTypeJson] }
+
+      get "/chores?done=is.false" `shouldRespondWith`
+        [json| [{"id": 2, "name": "do the laundry", "done": false }] |]
+        { matchHeaders = [matchContentTypeJson] }
+
+      get "/chores?done=is.unknown" `shouldRespondWith`
+        [json| [{"id": 3, "name": "wash the dishes", "done": null }] |]
+        { matchHeaders = [matchContentTypeJson] }
+
+    it "fails if 'is' used and there's no null or trilean value" $ do
+      get "/chores?done=is.nil" `shouldRespondWith` 400
+      get "/chores?done=is.ok"  `shouldRespondWith` 400
+
     it "matches with like" $ do
       get "/simple_pk?k=like.*yx" `shouldRespondWith`
         [json|[{"k":"xyyx","extra":"u"}]|]
diff --git a/test/fixtures/data.sql b/test/fixtures/data.sql
index d44f9e07e..71a0efe29 100644
--- a/test/fixtures/data.sql
+++ b/test/fixtures/data.sql
@@ -727,3 +727,6 @@ INSERT INTO test.contact (id,name, clientid) values (1,'Wally Walton',1),(2,'Wil
 
 TRUNCATE TABLE test.clientinfo CASCADE;
 INSERT INTO test.clientinfo (id,clientid, other) values (1,1,'123 Main St'),(2,2,'456 South 3rd St'),(3,3,'789 Palm Tree Ln');
+
+TRUNCATE TABLE test.chores CASCADE;
+INSERT INTO test.chores (id, name, done) values (1, 'take out the garbage', true), (2, 'do the laundry', false), (3, 'wash the dishes', null);
diff --git a/test/fixtures/privileges.sql b/test/fixtures/privileges.sql
index df5311e89..b103eeae3 100644
--- a/test/fixtures/privileges.sql
+++ b/test/fixtures/privileges.sql
@@ -159,6 +159,7 @@ GRANT ALL ON TABLE
     , client
     , clientinfo
     , contact
+    , chores
 TO postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;
@@ -213,4 +214,4 @@ DO $do$BEGIN
     GRANT ALL ON TABLE test.car_models_car_dealers_10to20 TO postgrest_test_anonymous;
     GRANT ALL ON TABLE test.car_models_car_dealers_default TO postgrest_test_anonymous;
   END IF;
-END$do$;
\ No newline at end of file
+END$do$;
diff --git a/test/fixtures/schema.sql b/test/fixtures/schema.sql
index fe60d9e92..ba1fe6a07 100644
--- a/test/fixtures/schema.sql
+++ b/test/fixtures/schema.sql
@@ -2417,3 +2417,9 @@ CREATE TABLE clientinfo (
 , clientid int unique references client(id)
 , other text
 );
+
+CREATE TABLE chores (
+  id int primary key
+, name text
+, done bool
+);