diff --git a/docs/Config_Changes.md b/docs/Config_Changes.md
index 13257326..3c14307e 100644
--- a/docs/Config_Changes.md
+++ b/docs/Config_Changes.md
@@ -6,6 +6,10 @@ All dates in this document are approximate.
 
 # Changes
 
+20200902: The RTD resistance-to-temperature calculation for MAX31865
+converters has been corrected to not read low.  If you are using such a
+device, you should recalibrate your print temperature and PID settings.
+
 20200816: The gcode macro `printer.gcode` object has been renamed to
 `printer.gcode_move`.  Several undocumented variables in
 `printer.toolhead` and `printer.gcode` have been removed.  See
diff --git a/klippy/extras/spi_temperature.py b/klippy/extras/spi_temperature.py
index d6f0a2ba..c7ae77a8 100644
--- a/klippy/extras/spi_temperature.py
+++ b/klippy/extras/spi_temperature.py
@@ -268,7 +268,7 @@ MAX31865_FAULT_RTDINLOW        = 0x08
 MAX31865_FAULT_OVUV            = 0x04
 
 VAL_A = 0.00390830
-VAL_B = 0.0000005775
+VAL_B = -0.0000005775
 VAL_C = -0.00000000000418301
 VAL_ADC_MAX = 32768.0 # 2^15