diff --git a/Docs/src/log.but b/Docs/src/log.but
index 967acecb..dc4c6885 100644
--- a/Docs/src/log.but
+++ b/Docs/src/log.but
@@ -4,7 +4,7 @@
 
 \c on|off
 
-Sets whether install logging to $INSTDIR\\install.log will happen. Note that \e{NSIS_CONFIG_LOG} must be set in the installer configuration (it is not by default) to support this.
+Sets whether install logging to $INSTDIR\\install.log will happen. $INSTDIR must have a value before you call this function or it will not work. Note that \e{NSIS_CONFIG_LOG} must be set in the installer configuration (it is not by default) to support this.
 
 \S2{logtext} LogText