diff --git a/package/base-files/files/bin/ipcalc.sh b/package/base-files/files/bin/ipcalc.sh
index e8c7a07df6..c698224f19 100755
--- a/package/base-files/files/bin/ipcalc.sh
+++ b/package/base-files/files/bin/ipcalc.sh
@@ -2,8 +2,6 @@
 
 . /lib/functions/ipv4.sh
 
-PROG="$(basename "$0")"
-
 # wrapper to convert an integer to an address, unless we're using
 # decimal output format.
 # hook for library function
@@ -21,7 +19,7 @@ _ip2str() {
 }
 
 usage() {
-    echo "Usage: $PROG [ -d | -x ] address/prefix [ start limit ]" >&2
+    echo "Usage: ${0##*/} [ -d | -x ] address/prefix [ start limit ]" >&2
     exit 1
 }