diff --git a/Docs/src/sec.but b/Docs/src/sec.but
index dee29639..d86dbaf3 100644
--- a/Docs/src/sec.but
+++ b/Docs/src/sec.but
@@ -149,7 +149,7 @@ Sets the current \R{ainsttype}{InstType}. inst_type_idx should be between 0 and
 
 \c user_var
 
-Get the current \R{ainsttype}{InstType} and stores it in user_var. If the first install type is selected, 0 will be put in user_var. If the second install type is selected, 1 will be put in user_var, and so on. The value of $\{NSIS_MAX_INST_TYPES\} (32 by default) means that the custom install type was selected.
+Get the current \R{ainsttype}{InstType} and stores it in user_var. If the first install type is selected, 0 will be put in user_var. If the second install type is selected, 1 will be put in user_var, and so on. The value of $\{NSIS_MAX_INST_TYPES\} (32 by default) means that the user selected a custom set of sections. Note that simply selecting "Custom" in the drop-down menu is not enough to trigger this. The value is calculated by the sections actually selected.
 
 \S2{sinsttypesettext} InstTypeSetText