diff --git a/CHANGELOG.md b/CHANGELOG.md
index c5330fd85c4..326a2a06008 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,7 @@
 
 ### vNEXT
 
-* ...
+* Fix `delegateToSchema.js` to accept and move forward args with zero or false values [PR #586](https://github.com/apollographql/graphql-tools/pull/586)
 
 ### v2.18.0
 
diff --git a/src/stitching/delegateToSchema.ts b/src/stitching/delegateToSchema.ts
index f8214167e03..4e64f7a67f6 100644
--- a/src/stitching/delegateToSchema.ts
+++ b/src/stitching/delegateToSchema.ts
@@ -72,18 +72,15 @@ export default async function delegateToSchema(
     if (
       operationDefinition &&
       operationDefinition.kind === Kind.OPERATION_DEFINITION &&
-      operationDefinition.variableDefinitions
+      operationDefinition.variableDefinitions &&
+      Array.isArray(operationDefinition.variableDefinitions)
     ) {
-      operationDefinition.variableDefinitions.forEach(definition => {
+      for (const definition of operationDefinition.variableDefinitions) {
         const key = definition.variable.name.value;
         // (XXX) This is kinda hacky
-        let actualKey = key;
-        if (actualKey.startsWith('_')) {
-          actualKey = actualKey.slice(1);
-        }
-        const value = args[actualKey] || args[key] || info.variableValues[key];
-        variableValues[key] = value;
-      });
+        const actualKey = key.startsWith('_') ? key.slice(1) : key;
+        variableValues[key] = args[actualKey] != null ? args[actualKey] : info.variableValues[key];
+      }
     }
 
     if (operation === 'query' || operation === 'mutation') {
diff --git a/src/test/testMergeSchemas.ts b/src/test/testMergeSchemas.ts
index cce1678ceb5..34b5d734951 100644
--- a/src/test/testMergeSchemas.ts
+++ b/src/test/testMergeSchemas.ts
@@ -1143,21 +1143,21 @@ bookingById(id: "b1") {
     describe('variables', () => {
       it('basic', async () => {
         const propertyFragment = `
-propertyById(id: $p1) {
-  id
-  name
-}
-  `;
+          propertyById(id: $p1) {
+            id
+            name
+          }
+        `;
         const bookingFragment = `
-bookingById(id: $b1) {
-  id
-  customer {
-    name
-  }
-  startTime
-  endTime
-}
-  `;
+          bookingById(id: $b1) {
+            id
+            customer {
+              name
+            }
+            startTime
+            endTime
+          }
+        `;
 
         const propertyResult = await graphql(
           propertySchema,