diff --git a/docs/reference.md b/docs/reference.md
index b4792a6..a90afb7 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -67,7 +67,9 @@ Zero if the switch is current turned off, non-zero otherwise.
 Mode: Read/write
 
 Power will be maintained for this long after the switch has been
-turned off.
+turned off.  The maximum value is 3276.7s, all register scalings
+report in units of 100ms (thus int8 will not be able to command or
+monitor the full possible scale).
 
 ### 0x004 - Boot time ###
 
diff --git a/fw/power_dist.cc b/fw/power_dist.cc
index 12f608e..9d9a96a 100644
--- a/fw/power_dist.cc
+++ b/fw/power_dist.cc
@@ -101,9 +101,9 @@ Value ScaleVoltage(float value, size_t type) {
   return ScaleMapping(value, 0.5f, 0.1f, 0.001f, type);
 }
 
-int8_t ReadIntMapping(Value value) {
+int16_t ReadInt16Mapping(Value value) {
   return std::visit([](auto a) {
-      return static_cast<int8_t>(a);
+      return static_cast<int16_t>(a);
     }, value);
 }
 
@@ -514,7 +514,7 @@ class PowerDist : public mjlib::multiplex::MicroServer::Server {
         return 2;
       }
       case Register::kLockTime: {
-        status_.lock_time_100ms = ReadIntMapping(value);
+        status_.lock_time_100ms = ReadInt16Mapping(value);
         return 0;
       }
       case Register::kFaultCode:
@@ -547,10 +547,10 @@ class PowerDist : public mjlib::multiplex::MicroServer::Server {
         return IntMapping(static_cast<int8_t>(status_.switch_status), type);
       }
       case Register::kLockTime: {
-        return IntMapping(static_cast<int8_t>(status_.lock_time_100ms), type);
+        return IntMapping(static_cast<int16_t>(status_.lock_time_100ms), type);
       }
       case Register::kBootTime: {
-        return IntMapping(static_cast<int8_t>(0), type);
+        return IntMapping(static_cast<int16_t>(0), type);
       }
       case Register::kOutputVoltage: {
         return ScaleVoltage(status_.output_voltage_V, type);