diff --git a/Makefile.in b/Makefile.in
index 2fc4d8ec299788ac45c9f2f80590fd38079848dc..3b8a4351371a031e2b3c8035b4b442137e959a44 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,6 +1,6 @@
 CXX = @CXX@
 CXXFLAGS = @CXXFLAGS@
-CPPFLAGS = @CPPFLAGS@ @DEFS@
+CPPFLAGS = -DNDEBUG @CPPFLAGS@ @DEFS@
 LDFLAGS = @LDFLAGS@
 
 FLEX = @FLEX@