diff --git a/src/testdir/test_increment.in b/src/testdir/test_increment.in
index fb7e6e3..ecbc6f9 100644
--- a/src/testdir/test_increment.in
+++ b/src/testdir/test_increment.in
@@ -268,7 +268,15 @@
  Expected:
  1) <Ctrl-V>j$ <ctrl-a>
  2
- 1b
+ 2a
+
+20) increment a single letter
+Text:
+ a
+
+ Expected:
+ 1) <Ctrl-a> and cursor is on a
+ b
    
 
 
@@ -386,6 +394,13 @@
 k$
 :set nrformats&vim
 
+:" Test 20
+:set nrformats+=alpha
+:/^S20=/+,/^E20=/-y a
+:/^E20=/+put a
+:.put =col('.')
+:set nrformats&vim
+
 :" Save the report
 :/^# Test 1/,$w! test.out
 :qa!
@@ -572,6 +587,13 @@
 
 
 
+# Test 20
+S20====
+a
+E20====
+
+
+
 
 ENDTEST