NDEBUG stands for NO DEBUG...

Module.mk

@@ -59,9 +59,13 @@ CLINGLDFLAGSEXTRA := -Wl,--no-ctors-in-init-array
 endif
 
 # Define NDEBUG for consistency with llvm and clang.
+CLINGCXXNDEBUG := -DNDEBUG
 ifeq ($(ROOTBUILD),debug)
-CLINGCXXFLAGS += -DNDEBUG
+ifneq($(LLVMDEV),)
+CLINGCXXNDEBUG := 
 endif
+endif
+CLINGCXXFLAGS += $(CLINGCXXNDEBUG)
 
 ifeq ($(ARCH),win32gcc)
 # Hide llvm / clang symbols:

lib/Interpreter/Transaction.cpp

@@ -75,7 +75,7 @@ namespace cling {
     if (!m_DeclQueue)
       m_DeclQueue.reset(new DeclQueue());
 
-#ifdef NDEBUG
+#ifndef NDEBUG
     // Check for duplicates
     for (size_t i = 0, e = m_DeclQueue->size(); i < e; ++i)
       assert((*m_DeclsQueue)[i] != DCI && "Duplicates?!");