diff --git a/pid/zone.hpp b/pid/zone.hpp
index 2854997..464e672 100644
--- a/pid/zone.hpp
+++ b/pid/zone.hpp
@@ -71,6 +71,7 @@
     bool getRedundantWrite(void) const override;
     void setManualMode(bool mode);
     bool getFailSafeMode(void) const override;
+    void markSensorMissing(const std::string& name);
 
     int64_t getZoneID(void) const override;
     void addSetPoint(double setPoint, const std::string& name) override;
@@ -99,8 +100,8 @@
     double getCachedValue(const std::string& name) override;
     ValueCacheEntry getCachedValues(const std::string& name) override;
 
-    void addFanInput(const std::string& fan);
-    void addThermalInput(const std::string& therm);
+    void addFanInput(const std::string& fan, bool missingAcceptable);
+    void addThermalInput(const std::string& therm, bool missingAcceptable);
 
     void initializeLog(void) override;
     void writeLog(const std::string& value) override;
@@ -166,7 +167,8 @@
             // check if fan fail.
             if (sensor->getFailed())
             {
-                _failSafeSensors.insert(sensorInput);
+                markSensorMissing(sensorInput);
+
                 if (debugEnabled)
                 {
                     std::cerr << sensorInput << " sensor get failed\n";
@@ -174,7 +176,8 @@
             }
             else if (timeout != 0 && duration >= period)
             {
-                _failSafeSensors.insert(sensorInput);
+                markSensorMissing(sensorInput);
+
                 if (debugEnabled)
                 {
                     std::cerr << sensorInput << " sensor timeout\n";
@@ -191,6 +194,7 @@
                         std::cerr << sensorInput
                                   << " is erased from failsafe sensor set\n";
                     }
+
                     _failSafeSensors.erase(kt);
                 }
             }
@@ -213,6 +217,7 @@
     const conf::CycleTime _cycleTime;
 
     std::set<std::string> _failSafeSensors;
+    std::set<std::string> _missingAcceptable;
 
     std::vector<double> _SetPoints;
     std::vector<double> _RPMCeilings;