diff --git a/README.md b/README.md
index 5e4481c..a56a93d 100644
--- a/README.md
+++ b/README.md
@@ -130,6 +130,13 @@ Note also that all the `LP_ENABLE_…` variables override the templates,
 i.e. if you use `$LP_BATT` in your template and you set `LP_ENABLE_BATT=0`
 in your config file, you will not have the battery informations.
 
+If you are using bash and want to use the `PROMPT_DIRTRIM` built-in
+functionality to shorten but still have liquidprompt calculating the number of
+directories to keep in the path, precise a value for `PROMPT_DIRTRIM` before
+sourcing liquidprompt and liquidprompt will override this value with one
+fitting the width of your terminal.
+
+
 ## CUSTOMIZING THE PROMPT
 
 ### ADD A PS1 PREFIX
diff --git a/liquidprompt b/liquidprompt
index c328ff0..ce61fba 100755
--- a/liquidprompt
+++ b/liquidprompt
@@ -490,7 +490,10 @@ _lp_shorten_path()
     fi
 }
 
-
+# In bash shell, PROMPT_DIRTRIM is the number of directory to keep at the end
+# of the displayed path (if "\w" is present in the PS1 var).
+# liquidprompt can calculate this number under two condition, path shortening
+# must be activated and PROMPT_DIRTRIM must be already set.
 _lp_get_dirtrim() {
     [[ "$LP_ENABLE_SHORTEN_PATH" != 1 ]] && echo 0 && return