diff --git a/config.h.in b/config.h.in
index 232e731..9e587bf 100644
--- a/config.h.in
+++ b/config.h.in
@@ -91,3 +91,5 @@ char *strstr(const char *, const char *);
 # ifndef HAVE_STRTOL
 long strtol(const char *, char **, int);
 # endif
+
+#define USE_INTERP_RESULT 1