diff --git a/pvlib/temperature.py b/pvlib/temperature.py
index 03871143e8..663f068dab 100644
--- a/pvlib/temperature.py
+++ b/pvlib/temperature.py
@@ -316,7 +316,8 @@ def pvsyst_cell(poa_global, temp_air, wind_speed=1.0, u_c=29.0, u_v=0.0,
         :math:`\left[ \frac{\text{W}/\text{m}^2}{\text{C}\ \left( \text{m/s} \right)} \right]`
 
     eta_m : numeric, default 0.1
-        Module external efficiency as a fraction, i.e., DC power / poa_global.
+        Module external efficiency as a fraction, i.e.,
+        :math:`DC\ power / (POA\ irradiance \times module\ area)`.
         Parameter :math:`\eta_{m}` in :eq:`pvsyst`.
 
     alpha_absorption : numeric, default 0.9