diff --git a/mainloop.cpp b/mainloop.cpp
index cfa5483..dfba15f 100644
--- a/mainloop.cpp
+++ b/mainloop.cpp
@@ -157,6 +157,16 @@
 
 int64_t adjustValue(const SensorSet::key_type& sensor, int64_t value)
 {
+// Because read doesn't have an out pointer to store errors.
+// let's assume negative values are errors if they have this
+// set.
+#ifdef NEGATIVE_ERRNO_ON_FAIL
+    if (value < 0)
+    {
+        return value;
+    }
+#endif
+
     const auto& it = sensorAdjusts.find(sensor);
     if (it != sensorAdjusts.end())
     {