diff --git a/src/configure b/src/configure
index 6aa15be..f9f65fa 100755
--- a/src/configure
+++ b/src/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # run the automatically generated configure script
 CONFIG_STATUS=auto/config.status \
-	auto/configure "$@" --srcdir="${srcdir-.}" --cache-file=auto/config.cache
+	auto/configure "$@" --srcdir="${srcdir:-.}" --cache-file=auto/config.cache
 # Stupid autoconf 2.5x causes this file to be left behind.
 if test -f configure.lineno; then rm -f configure.lineno; fi