diff --git a/packages/survey-core/src/helpers.ts b/packages/survey-core/src/helpers.ts
index 14513b6fb4..7d2649af24 100644
--- a/packages/survey-core/src/helpers.ts
+++ b/packages/survey-core/src/helpers.ts
@@ -215,11 +215,13 @@ export class Helpers {
   }
   private static getNumberCore(value: any): number {
     if (typeof value == "string") {
-      if(!value.trim()) return NaN;
+      value = value.trim();
+      if(!value) return NaN;
       if(value.indexOf("0x") == 0) {
         if(value.length > 32) return NaN;
         return parseInt(value);
       }
+      if(value.length > 15 && Helpers.isDigitsOnly(value)) return NaN;
       if(Helpers.isStringHasOperator(value)) return NaN;
     }
     value = this.prepareStringToNumber(value);
@@ -320,6 +322,13 @@ export class Helpers {
   public static isCharDigit(ch: string): boolean {
     return ch >= "0" && ch <= "9";
   }
+  public static isDigitsOnly(str: string): boolean {
+    if(!str) return false;
+    for(let i = 0; i < str.length; i ++) {
+      if(!Helpers.isCharDigit(str[i])) return false;
+    }
+    return true;
+  }
   private static getNumberFromStr(str: string, index: number): number {
     if(!this.isCharDigit(str[index])) return NaN;
     let nStr = "";
diff --git a/packages/survey-core/tests/expressions/expressionParserTest.ts b/packages/survey-core/tests/expressions/expressionParserTest.ts
index 3083fe319d..98a743cb4f 100644
--- a/packages/survey-core/tests/expressions/expressionParserTest.ts
+++ b/packages/survey-core/tests/expressions/expressionParserTest.ts
@@ -1683,3 +1683,10 @@ QUnit.test("ExpressionRunner: apply custom converter, #8634", function(assert) {
 
   settings.parseNumber = oldCallback;
 });
+QUnit.test("ExpressionRunner: do not convert to number extreme large strings", function(assert) {
+  const runner = new ExpressionRunner("{a} + 2");
+  const values: any = { a: "999999999999999" };
+  assert.strictEqual(runner.run(values), 1000000000000001, "it is a number");
+  values.a = "9999999999999999";
+  assert.strictEqual(runner.run(values), "99999999999999992", "it is a string");
+});