diff --git a/src/scripting_api/aform.js b/src/scripting_api/aform.js
index 1f3b0a155..7045cd990 100644
--- a/src/scripting_api/aform.js
+++ b/src/scripting_api/aform.js
@@ -414,6 +414,9 @@ class AForm {
     const values = [];
     for (const cField of cFields) {
       const field = this._document.getField(cField);
+      if (!field) {
+        continue;
+      }
       const number = this.AFMakeNumber(field.value);
       if (number !== null) {
         values.push(number);
diff --git a/test/unit/scripting_spec.js b/test/unit/scripting_spec.js
index fadc22bc9..a6a5debec 100644
--- a/test/unit/scripting_spec.js
+++ b/test/unit/scripting_spec.js
@@ -1061,7 +1061,7 @@ describe("Scripting", function () {
                 value: "",
                 actions: {
                   Calculate: [
-                    `AFSimple_Calculate("SUM", ["field1", "field2", "field3"]);`,
+                    `AFSimple_Calculate("SUM", ["field1", "field2", "field3", "unknown"]);`,
                   ],
                 },
                 type: "text",