diff --git a/configure.in b/configure.in
index ede5e0c..18f803c 100644
--- a/configure.in
+++ b/configure.in
@@ -8,6 +8,7 @@
 
 # We want these before the checks, so the checks can modify their values.
 test -z "$LDLIBS" && LDLIBS=-lm AC_SUBST(LDLIBS)
+test -z "$PROGEXT" && PROGEXT="" AC_SUBST(PROGEXT)
 
 dnl **** Command-line arguments ****