diff --git a/runtime/doc/motion.txt b/runtime/doc/motion.txt
index 448b68b..8c07fbf 100644
--- a/runtime/doc/motion.txt
+++ b/runtime/doc/motion.txt
@@ -600,7 +600,8 @@
 i[			"inner [] block", select [count] '[' ']' blocks.  This
 			goes backwards to the [count] unclosed '[', and finds
 			the matching ']'.  The enclosed text is selected,
-			excluding the '[' and ']'.  The |cpo-M| option flag
+			excluding the '[' and ']'.  It's an error to select an
+			empty inner block like "[]".  The |cpo-M| option flag
 			is used to handle escaped brackets.
 			When used in Visual mode it is made characterwise.
 
@@ -618,7 +619,8 @@
 ib			"inner block", select [count] blocks, from "[count] [("
 			to the matching ')', excluding the '(' and ')' (see
 			|[(|).  If the cursor is not inside a () block, then
-			find the next "(".  The |cpo-M| option flag
+			find the next "(".  It's an error to select an empty
+			inner block like "()".  The |cpo-M| option flag
 			is used to handle escaped parenthesis.
 			When used in Visual mode it is made characterwise.
 
@@ -632,8 +634,9 @@
 i>						*v_i>* *v_i<* *i>* *i<*
 i<			"inner <> block", select [count] <> blocks, from
 			the [count]'th unmatched '<' backwards to the matching
-			'>', excluding the '<' and '>'.  The |cpo-M| option flag
-			is used to handle escaped '<' and '>'.
+			'>', excluding the '<' and '>'.  It's an error to
+			select an empty inner block like "<>".  The |cpo-M|
+			option flag is used to handle escaped '<' and '>'.
 			When used in Visual mode it is made characterwise.
 
 						*v_at* *at*
@@ -663,7 +666,8 @@
 i{							*v_iB* *v_i{* *iB*
 iB			"inner Block", select [count] Blocks, from "[count] [{"
 			to the matching '}', excluding the '{' and '}' (see
-			|[{|).  The |cpo-M| option flag is used to handle
+			|[{|).  It's an error to select an empty inner block
+			like "{}".  The |cpo-M| option flag is used to handle
 			escaped braces.
 			When used in Visual mode it is made characterwise.