diff --git a/src/PostgREST/ApiRequest/Types.hs b/src/PostgREST/ApiRequest/Types.hs
index e4fb6dc323..e5eb0bf139 100644
--- a/src/PostgREST/ApiRequest/Types.hs
+++ b/src/PostgREST/ApiRequest/Types.hs
@@ -86,7 +86,6 @@ data ApiRequestError
   | PutLimitNotAllowedError
   | QueryParamError QPError
   | RelatedOrderNotToOne Text Text
-  | SpreadNotToOne Text Text
   | UnacceptableFilter Text
   | UnacceptableSchema [Text]
   | UnsupportedMethod ByteString
@@ -145,7 +144,7 @@ type Cast = Text
 type Alias = Text
 type Hint = Text
 
-data AggregateFunction = Sum | Avg | Max | Min | Count
+data AggregateFunction = Sum | Avg | Max | Min | Count | JsonAgg
   deriving (Show, Eq)
 
 data EmbedParam
diff --git a/src/PostgREST/Error.hs b/src/PostgREST/Error.hs
index 9c7d6d3a6f..09aa3bf7a0 100644
--- a/src/PostgREST/Error.hs
+++ b/src/PostgREST/Error.hs
@@ -80,7 +80,6 @@ instance PgrstError ApiRequestError where
   status PutLimitNotAllowedError     = HTTP.status400
   status QueryParamError{}           = HTTP.status400
   status RelatedOrderNotToOne{}      = HTTP.status400
-  status SpreadNotToOne{}            = HTTP.status400
   status UnacceptableFilter{}        = HTTP.status400
   status UnacceptableSchema{}        = HTTP.status406
   status UnsupportedMethod{}         = HTTP.status405
@@ -176,12 +175,6 @@ instance JSON.ToJSON ApiRequestError where
     (Just $ JSON.String $ "'" <> origin <> "' and '" <> target <> "' do not form a many-to-one or one-to-one relationship")
     Nothing
 
-  toJSON (SpreadNotToOne origin target) = toJsonPgrstError
-    ApiRequestErrorCode19
-    ("A spread operation on '" <> target <> "' is not possible")
-    (Just $ JSON.String $ "'" <> origin <> "' and '" <> target <> "' do not form a many-to-one or one-to-one relationship")
-    Nothing
-
   toJSON (UnacceptableFilter target) = toJsonPgrstError
     ApiRequestErrorCode20
     ("Bad operator on the '" <> target <> "' embedded resource")
diff --git a/src/PostgREST/Plan.hs b/src/PostgREST/Plan.hs
index 2e3587e988..4f2f0ff84a 100644
--- a/src/PostgREST/Plan.hs
+++ b/src/PostgREST/Plan.hs
@@ -336,10 +336,10 @@ readPlan qi@QualifiedIdentifier{..} AppConfig{configDbMaxRows, configDbAggregate
     validateAggFunctions configDbAggregates =<<
     addRelSelects =<<
     addNullEmbedFilters =<<
-    validateSpreadEmbeds =<<
     addRelatedOrders =<<
     addAliases =<<
     expandStars ctx =<<
+    addJsonAggToManySpread False =<<
     addRels qiSchema (iAction apiRequest) dbRelationships Nothing =<<
     addLogicTrees ctx apiRequest =<<
     addRanges apiRequest =<<
@@ -604,6 +604,22 @@ findRel schema allRels origin target hint =
             )
       ) $ fromMaybe mempty $ HM.lookup (QualifiedIdentifier schema origin, schema) allRels
 
+-- Add JsonAgg aggregates to selected fields that do not have other aggregates and:
+-- * Belong to a spread to-many relationship
+-- * Are to-one spread but are nested inside a spread to-many relationship
+addJsonAggToManySpread :: Bool -> ReadPlanTree -> Either ApiRequestError ReadPlanTree
+addJsonAggToManySpread isNestedInToManyRel (Node rp@ReadPlan{select, relIsSpread, relToParent} forest) =
+  let shouldAddJsonAgg = relIsSpread && (isNestedInToManyRel || Just False == (relIsToOne <$> relToParent))
+      newForest = rights $ addJsonAggToManySpread shouldAddJsonAgg <$> forest
+      newSelects
+        | shouldAddJsonAgg = fieldToJsonAgg <$> select
+        | otherwise = select
+  in Right $ Node rp { select = newSelects } newForest
+  where
+    fieldToJsonAgg field
+      | isJust $ csAggFunction field = field
+      | otherwise = field { csAggFunction = Just JsonAgg, csAlias = newAlias (csAlias field) (cfName $ csField field) }
+    newAlias alias fieldName = maybe (Just fieldName) pure alias
 
 addRelSelects :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
 addRelSelects node@(Node rp forest)
@@ -896,15 +912,6 @@ resolveLogicTree ctx (Expr b op lts) = CoercibleExpr b op (map (resolveLogicTree
 resolveFilter :: ResolverContext -> Filter -> CoercibleFilter
 resolveFilter ctx (Filter fld opExpr) = CoercibleFilter{field=resolveQueryInputField ctx fld, opExpr=opExpr}
 
--- Validates that spread embeds are only done on to-one relationships
-validateSpreadEmbeds :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
-validateSpreadEmbeds (Node rp@ReadPlan{relToParent=Nothing} forest) = Node rp <$> validateSpreadEmbeds `traverse` forest
-validateSpreadEmbeds (Node rp@ReadPlan{relIsSpread,relToParent=Just rel,relName} forest) = do
-  validRP <- if relIsSpread && not (relIsToOne rel)
-    then Left $ SpreadNotToOne (qiName $ relTable rel) relName -- TODO using relTable is not entirely right because ReadPlan might have an alias, need to store the parent alias on ReadPlan
-    else Right rp
-  Node validRP <$> validateSpreadEmbeds `traverse` forest
-
 -- Find a Node of the Tree and apply a function to it
 updateNode :: (a -> ReadPlanTree -> ReadPlanTree) -> (EmbedPath, a) -> Either ApiRequestError ReadPlanTree -> Either ApiRequestError ReadPlanTree
 updateNode f ([], a) rr = f a <$> rr
diff --git a/src/PostgREST/Query/SqlFragment.hs b/src/PostgREST/Query/SqlFragment.hs
index 39b869d5d9..7f954ccfaf 100644
--- a/src/PostgREST/Query/SqlFragment.hs
+++ b/src/PostgREST/Query/SqlFragment.hs
@@ -283,10 +283,12 @@ pgFmtApplyAggregate Nothing _ snippet = snippet
 pgFmtApplyAggregate (Just agg) aggCast snippet =
   pgFmtApplyCast aggCast aggregatedSnippet
   where
+    aggregatedSnippet = convertAggFunction agg <> "(" <> snippet <> ")"
     convertAggFunction :: AggregateFunction -> SQL.Snippet
     -- Convert from e.g. Sum (the data type) to SUM
-    convertAggFunction = SQL.sql . BS.map toUpper . BS.pack . show
-    aggregatedSnippet = convertAggFunction agg <> "(" <> snippet <> ")"
+    convertAggFunction = \case
+      JsonAgg -> SQL.sql "json_agg"
+      a       -> SQL.sql . BS.map toUpper . BS.pack $ show a
 
 pgFmtApplyCast :: Maybe Cast -> SQL.Snippet -> SQL.Snippet
 pgFmtApplyCast Nothing snippet = snippet
diff --git a/test/spec/Feature/Query/AggregateFunctionsSpec.hs b/test/spec/Feature/Query/AggregateFunctionsSpec.hs
index 5c9a6488c0..701599dc06 100644
--- a/test/spec/Feature/Query/AggregateFunctionsSpec.hs
+++ b/test/spec/Feature/Query/AggregateFunctionsSpec.hs
@@ -211,6 +211,58 @@ allowed =
             {"name": "Sarah", "process_supervisor": [{"category": "Batch", "cost_sum": 180.00}]}]|]
           { matchHeaders = [matchContentTypeJson] }
 
+    context "performing json_agg() aggregations on to-many spread embeds" $ do
+      it "works on a one-to-many relationship" $ do
+        get "/clients?select=id,...projects(name)" `shouldRespondWith`
+          [json|[
+            {"id":1,"name":["Windows 7", "Windows 10"]},
+            {"id":2,"name":["IOS", "OSX"]}
+          ]|]
+          { matchStatus  = 200
+          , matchHeaders = [matchContentTypeJson]
+          }
+-- Nested not working as expected:
+--        get "/entities?select=name,...child_entities(child_name:name,...grandchild_entities(grandchild_name:name))&limit=3" `shouldRespondWith`
+--          [json|[
+--            {"name":"entity 1","child_name":"child entity 1","grandchild_name":"grandchild entity 1"},
+--            {"name":"entity 2","child_name":"child entity 1","grandchild_name":"grandchild entity 1"},
+--            {"name":"entity 3","child_name":"child entity 2","grandchild_name":"grandchild entity 1"}
+--          ]|]
+--          { matchStatus  = 200
+--          , matchHeaders = [matchContentTypeJson]
+--          }
+--        get "/videogames?select=name,...computed_designers(designer_name:name)" `shouldRespondWith`
+--          [json|[
+--            {"name":"Civilization I","designer_name":"Sid Meier"},
+--            {"name":"Civilization II","designer_name":"Sid Meier"},
+--            {"name":"Final Fantasy I","designer_name":"Hironobu Sakaguchi"},
+--            {"name":"Final Fantasy II","designer_name":"Hironobu Sakaguchi"}
+--          ]|]
+--          { matchStatus  = 200
+--          , matchHeaders = [matchContentTypeJson]
+--          }
+
+
+--      it "works inside a normal embed" $
+--        get "/grandchild_entities?select=name,child_entity:child_entities(name,...entities(parent_name:name))&limit=1" `shouldRespondWith`
+--          [json|[
+--            {"name":"grandchild entity 1","child_entity":{"name":"child entity 1","parent_name":"entity 1"}}
+--          ]|]
+--          { matchStatus  = 200
+--          , matchHeaders = [matchContentTypeJson]
+--          }
+
+      it "works on a many-to-many relationship" $
+        get "/users?select=name,...projects(projects:name)" `shouldRespondWith`
+          [json|[
+            {"name":"Dwight Schrute","projects":["Windows 7", "IOS"]},
+            {"name":"Angela Martin","projects":["Windows 7", "Windows 10"]},
+            {"name":"Michael Scott","projects":["IOS", "OSX"]}
+          ]|]
+          { matchStatus  = 200
+          , matchHeaders = [matchContentTypeJson]
+          }
+
 disallowed :: SpecWith ((), Application)
 disallowed =
   describe "attempting to use an aggregate when aggregate functions are disallowed" $ do
diff --git a/test/spec/Feature/Query/SpreadQueriesSpec.hs b/test/spec/Feature/Query/SpreadQueriesSpec.hs
index 07a9c9d6d7..73fc351da3 100644
--- a/test/spec/Feature/Query/SpreadQueriesSpec.hs
+++ b/test/spec/Feature/Query/SpreadQueriesSpec.hs
@@ -63,25 +63,25 @@ spec =
         , matchHeaders = [matchContentTypeJson]
         }
 
-    it "fails when is not a to-one relationship" $ do
+    it "fails when it's a to-many relationship and aggregates are disabled" $ do
       get "/clients?select=*,...projects(*)" `shouldRespondWith`
         [json|{
-          "code":"PGRST119",
-          "details":"'clients' and 'projects' do not form a many-to-one or one-to-one relationship",
           "hint":null,
-          "message":"A spread operation on 'projects' is not possible"
+          "details":null,
+          "code":"PGRST123",
+          "message":"Use of aggregate functions is not allowed"
         }|]
-        { matchStatus  = 400
+        { matchStatus = 400
         , matchHeaders = [matchContentTypeJson]
         }
       get "/designers?select=*,...computed_videogames(*)" `shouldRespondWith`
         [json|{
-          "code":"PGRST119",
-          "details":"'designers' and 'computed_videogames' do not form a many-to-one or one-to-one relationship",
           "hint":null,
-          "message":"A spread operation on 'computed_videogames' is not possible"
+          "details":null,
+          "code":"PGRST123",
+          "message":"Use of aggregate functions is not allowed"
         }|]
-        { matchStatus  = 400
+        { matchStatus = 400
         , matchHeaders = [matchContentTypeJson]
         }