diff --git a/packages/ra-data-graphql-simple/src/buildVariables.js b/packages/ra-data-graphql-simple/src/buildVariables.js
index ecd09b7819a..8e7b69c7564 100644
--- a/packages/ra-data-graphql-simple/src/buildVariables.js
+++ b/packages/ra-data-graphql-simple/src/buildVariables.js
@@ -25,7 +25,8 @@ const sanitizeValue = (type, value) => {
 };
 
 const castType = (value, type) => {
-    switch (`${type.kind}:${type.name}`) {
+    const realType = type.kind === 'NON_NULL' ? type.ofType : type;
+    switch (`${realType.kind}:${realType.name}`) {
         case 'SCALAR:Int':
             return Number(value);