diff --git a/src/engine/build.jam b/src/engine/build.jam
index 607b26e76..226986f42 100644
--- a/src/engine/build.jam
+++ b/src/engine/build.jam
@@ -273,7 +273,7 @@ else
 }
 
 # Debug assertions, or not.
-if ! $(debug) && ! --noassert in $(ARGV)
+if ! $(debug) || --noassert in $(ARGV)
 {
     --defs += NDEBUG ;
 }