diff --git a/gitstatus/gitstatus.prompt.sh b/gitstatus/gitstatus.prompt.sh
index 8ee28de0..f54c11ac 100644
--- a/gitstatus/gitstatus.prompt.sh
+++ b/gitstatus/gitstatus.prompt.sh
@@ -2,7 +2,7 @@
 
 # Source gitstatus.plugin.sh from $GITSTATUS_DIR or from the same directory
 # in which the current script resides if the variable isn't set.
-if [[ -n "${GITSTATUS_DIR:-}" ]]; then
+if [[ -n "${GITSTATUS_DIR-}" ]]; then
   source "$GITSTATUS_DIR"                           || return
 elif [[ "${BASH_SOURCE[0]}" == */* ]]; then
   source "${BASH_SOURCE[0]%/*}/gitstatus.plugin.sh" || return
@@ -85,7 +85,14 @@ function gitstatus_prompt_update() {
 gitstatus_stop && gitstatus_start -s -1 -u -1 -c -1 -d -1
 
 # On every prompt, fetch git status and set GITSTATUS_PROMPT.
-PROMPT_COMMAND=gitstatus_prompt_update
+if [[ -z "${PROMPT_COMMAND[*]}" ]]; then
+  PROMPT_COMMAND=gitstatus_prompt_update
+elif [[ ! "${PROMPT_COMMAND[*]}" =~ [[:space:]\;]?gitstatus_prompt_update[[:space:]\;]? ]]; then
+  # Note: If PROMPT_COMMAND is an array, this will modify its first element.
+  PROMPT_COMMAND=$'gitstatus_prompt_update\n'"$PROMPT_COMMAND"
+fi
+
+# Retain 3 trailing components of the current directory.
 PROMPT_DIRTRIM=3
 
 # Enable promptvars so that ${GITSTATUS_PROMPT} in PS1 is expanded.