1 files changed, 4 insertions, 1 deletions
diff --git a/zconfig.h b/zconfig.h
index c5cf2c3..96c0e45 100644
--- a/zconfig.h
+++ b/zconfig.h
@@ -44,6 +44,9 @@
  */
 /* #define CONFIG_ZAPTEL_MMX */
 
+/** If defined: the user must define exactly one ECHO_CAN_ var: */
+#ifndef ECHO_CAN_FROMENV 
+
 /*
  * Pick your echo canceller.
  * 
@@ -71,7 +74,7 @@
  * MARK2 echo canceller
  */
 /* #define AGGRESSIVE_SUPPRESSOR */
-
+#endif /* ifndef ECHO_CAN_FROMENV */
 /*
  * Define to turn off the echo canceler disable tone detector,
  * which will cause zaptel to ignore the 2100 Hz echo cancel disable