diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4f77ffa8..5f456a4f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,7 +8,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - uses: purescript-contrib/setup-purescript@main
+      - uses: purescript-contrib/setup-purescript@1.1
 
       - name: Cache PureScript dependencies
         uses: actions/cache@v2
diff --git a/src/GraphQL/Client/CodeGen/Schema.purs b/src/GraphQL/Client/CodeGen/Schema.purs
index 155cfb7c..f9690fef 100644
--- a/src/GraphQL/Client/CodeGen/Schema.purs
+++ b/src/GraphQL/Client/CodeGen/Schema.purs
@@ -20,7 +20,7 @@ import Data.List (List, mapMaybe)
 import Data.List as List
 import Data.Map (lookup)
 import Data.Map as Map
-import Data.Maybe (Maybe(..), maybe)
+import Data.Maybe (Maybe(..), fromMaybe, maybe)
 import Data.Monoid (guard)
 import Data.Newtype (unwrap)
 import Data.String (Pattern(..), codePointFromChar, contains, joinWith)
@@ -191,20 +191,23 @@ gqlToPursMainSchemaCode { externalTypes, fieldTypeOverrides, useNewtypesForRecor
 
   scalarTypeDefinitionToPurs :: AST.ScalarTypeDefinition -> String
   scalarTypeDefinitionToPurs (AST.ScalarTypeDefinition { description, name, directives }) =
-    guard (notElem tName builtInTypes) case lookup tName externalTypes of
-      Nothing -> unknownDebugMarker tName
-      Just external ->
-        descriptionToDocComment description
-          <> "type "
-          <> tName
-          <> " = "
-          <> external.moduleName
-          <> "."
-          <> external.typeName
+    guard (notElem tName builtInTypes)
+      $ descriptionToDocComment description
+      <> "type "
+      <> tName
+      <> " = "
+      <> typeAndModule.moduleName
+      <> "."
+      <> typeAndModule.typeName
     where
     tName = typeName name
 
-    unknownDebugMarker tn = "unknown type: " <> show tn
+    typeAndModule =
+      lookup tName externalTypes
+        # fromMaybe
+            { moduleName: "Data.Foreign"
+            , typeName: "Foreign -- Unknown scalar type. Add " <> tName <> " to externalTypes in codegen options override this behaviour"
+            }
 
   builtInTypes = [ "Int", "Number", "String", "Boolean" ]
 
diff --git a/test/GraphQL/Client/CodeGen/SchemaFromGqlToPurs.Test.purs b/test/GraphQL/Client/CodeGen/SchemaFromGqlToPurs.Test.purs
index d814c5bd..014bf724 100644
--- a/test/GraphQL/Client/CodeGen/SchemaFromGqlToPurs.Test.purs
+++ b/test/GraphQL/Client/CodeGen/SchemaFromGqlToPurs.Test.purs
@@ -262,6 +262,45 @@ instance argToGqlQuery :: (Newtype Query {| p},  RecordArg p a u) => ArgGql Quer
           )
             `
             result
+      it "handles unknown scalar types" do
+        let
+          gql =
+            """
+schema {
+  query: Query
+}
+
+type Query {
+  int: Int
+  my_type_a: SomethingUnknown!
+  my_type_b: SomethingElseUnknown
+  my_type_c: [AlsoUnkown!]!
+}
+
+scalar SomethingUnknown
+scalar SomethingElseUnknown
+scalar AlsoUnkown
+          """
+
+          result = """
+type Query = Query
+
+newtype Query = Query 
+  { int :: (Maybe Int)
+  , my_type_a :: SomethingUnknown
+  , my_type_b :: (Maybe SomethingElseUnknown)
+  , my_type_c :: (Array AlsoUnkown)
+  }
+derive instance newtypeQuery :: Newtype Query _
+instance argToGqlQuery :: (Newtype Query {| p},  RecordArg p a u) => ArgGql Query { | a }
+
+type SomethingUnknown = Data.Foreign.Foreign -- Unknown scalar type. Add SomethingUnknown to externalTypes in codegen options override this behaviour
+
+type SomethingElseUnknown = Data.Foreign.Foreign -- Unknown scalar type. Add SomethingElseUnknown to externalTypes in codegen options override this behaviour
+
+type AlsoUnkown = Data.Foreign.Foreign -- Unknown scalar type. Add AlsoUnkown to externalTypes in codegen options override this behaviour"""
+
+        gql `shouldParseTo` result
   where
   mkMap :: forall v. Array (Tuple String (Array (Tuple String v))) -> Map String (Map String v)
   mkMap = Map.fromFoldable >>> map Map.fromFoldable