diff --git a/ecmascript/builtins/builtins_string.cpp b/ecmascript/builtins/builtins_string.cpp
index 325a2dc492bf1c7c0542376086dd5a9211aeb4da..3edb6e60545e2d8f8e0e7407c34abbadf817033e 100644
--- a/ecmascript/builtins/builtins_string.cpp
+++ b/ecmascript/builtins/builtins_string.cpp
@@ -267,7 +267,7 @@ JSTaggedValue BuiltinsString::CharAt(EcmaRuntimeCallInfo *argv)
             return factory->GetEmptyString().GetTaggedValue();
         }
         pos = posVal.ToInt32();
-    }
+            }
     if (pos < 0 || pos >= thisLen) {
         return factory->GetEmptyString().GetTaggedValue();
     }
@@ -514,16 +514,19 @@ JSTaggedValue BuiltinsString::LastIndexOf(EcmaRuntimeCallInfo *argv)
         JSHandle<JSTaggedValue> posTag = BuiltinsString::GetCallArg(argv, 1);
         JSTaggedNumber posVal = JSTaggedValue::ToInteger(thread, posTag);
         RETURN_EXCEPTION_IF_ABRUPT_COMPLETION(thread);
-        if (std::isnan(JSTaggedValue::ToNumber(thread, posTag).GetNumber())) {
+        if (std::isnan(JSTaggedValue::ToNumber(thread, posTag).GetNumber())
+            || posVal.GetNumber() == BuiltinsNumber::POSITIVE_INFINITY) {
             pos = thisLen;
         } else {
-            pos = posVal.ToInt32();
+            // pos = posVal.ToInt32();
+            pos = base::NumberHelper::DoubleInRangeInt32(posVal.GetNumber());
         }
         RETURN_EXCEPTION_IF_ABRUPT_COMPLETION(thread);
     }
     pos = std::min(std::max(pos, 0), thisLen);
     int32_t res = EcmaStringAccessor::LastIndexOf(thread->GetEcmaVM(), thisHandle, searchHandle, pos);
-    if (res >= 0 && res < thisLen) {
+    if ((res >= 0 && res < thisLen)
+        || (EcmaStringAccessor(searchHandle).GetLength() == 0 && res == thisLen)) {
         return GetTaggedInt(res);
     }
     res = -1;