diff --git a/tstypes/type/directives.d.ts b/tstypes/type/directives.d.ts
index 9719bf600e..ca9091a31e 100644
--- a/tstypes/type/directives.d.ts
+++ b/tstypes/type/directives.d.ts
@@ -67,6 +67,4 @@ export const GraphQLDeprecatedDirective: GraphQLDirective;
  */
 export const specifiedDirectives: ReadonlyArray<GraphQLDirective>;
 
-export function isSpecifiedDirective(
-  directive: any,
-): directive is GraphQLDirective;
+export function isSpecifiedDirective(directive: any): boolean;
diff --git a/tstypes/type/scalars.d.ts b/tstypes/type/scalars.d.ts
index fe16fd5cad..c7374908fc 100644
--- a/tstypes/type/scalars.d.ts
+++ b/tstypes/type/scalars.d.ts
@@ -8,4 +8,4 @@ export const GraphQLID: GraphQLScalarType;
 
 export const specifiedScalarTypes: ReadonlyArray<GraphQLScalarType>;
 
-export function isSpecifiedScalarType(type: any): type is GraphQLScalarType;
+export function isSpecifiedScalarType(type: any): boolean;