diff --git a/SConstruct b/SConstruct
index 484a686e..baf1cf1a 100644
--- a/SConstruct
+++ b/SConstruct
@@ -201,13 +201,15 @@ Help(opts.GenerateHelpText(defenv))
 if defenv['TARGET_ARCH'] != 'x86':
 	defenv['UNICODE'] = True
 
+if defenv['DEBUG']:
+	defenv.Append(CPPDEFINES = ['DEBUG'])
+
 # add prefixes defines
 if 'NSIS_CONFIG_CONST_DATA_PATH' in defenv['NSIS_CPPDEFINES']:
 	defenv.Append(NSIS_CPPDEFINES = [('PREFIX_CONF', '"%s"' % defenv.subst('$PREFIX_CONF'))])
 	defenv.Append(NSIS_CPPDEFINES = [('PREFIX_DATA', '"%s"' % defenv.subst('$PREFIX_DATA'))])
 
 # Need this early for the config header files to be placed in
-
 if defenv['UNICODE']:
 	if defenv['DEBUG']:
 		defenv.Replace(BUILD_PREFIX = 'build/udebug')
diff --git a/Source/build.cpp b/Source/build.cpp
index f8f6e5c4..bce3fa0b 100644
--- a/Source/build.cpp
+++ b/Source/build.cpp
@@ -740,7 +740,10 @@ int CEXEBuild::datablock_optimize(int start_offset, int first_int)
   if (!this->build_optimize_datablock || this_len < (int) sizeof(int))
     return start_offset;
 
-  MMapBuf *db = (MMapBuf *) cur_datablock;
+#ifdef DEBUG
+  assert(dynamic_cast<MMapBuf*>(cur_datablock));
+#endif
+  MMapBuf *db = static_cast<MMapBuf*>(cur_datablock);
   db->setro(TRUE);
 
   cached_db_size *db_sizes = (cached_db_size *) this->cur_datablock_cache->get();
@@ -788,7 +791,10 @@ bool CEXEBuild::datablock_finddata(IMMap&mmap, int mmstart, int size, int*ofs)
 {
   const int first_int = size;
   size &= ~ 0x80000000;
-  MMapBuf *db = (MMapBuf *) cur_datablock;
+#ifdef DEBUG
+  assert(dynamic_cast<MMapBuf*>(cur_datablock));
+#endif
+  MMapBuf *db = static_cast<MMapBuf*>(cur_datablock);
   cached_db_size *db_sizes = (cached_db_size *) this->cur_datablock_cache->get();
   int db_sizes_num = this->cur_datablock_cache->getlen() / sizeof(cached_db_size);
   for (int i = 0; i < db_sizes_num; i++)
diff --git a/Source/exehead/Main.c b/Source/exehead/Main.c
index 08032c77..43fcf87f 100644
--- a/Source/exehead/Main.c
+++ b/Source/exehead/Main.c
@@ -372,7 +372,7 @@ void NSISCALL CleanUp()
   // Clean up after plug-ins
   myDelete(state_plugins_dir, DEL_DIR | DEL_RECURSE | DEL_REBOOT);
 #endif // NSIS_CONFIG_PLUGIN_SUPPORT
-#ifdef _DEBUG
+#ifdef DEBUG
   // GlobalFree(g_header); ?
 #endif
 }
diff --git a/Source/makenssi.cpp b/Source/makenssi.cpp
index c8279971..76e5a23b 100644
--- a/Source/makenssi.cpp
+++ b/Source/makenssi.cpp
@@ -303,8 +303,10 @@ static inline int makensismain(int argc, TCHAR **argv)
 #ifdef _WIN32
   signed char outputbom=1;
 
+#ifdef DEBUG
   assert(CP_ACP == outputenc.GetCodepage()); // Required by CEXEBuild::notify() char* legacy handling.
 #endif
+#endif //~ _WIN32
 
   // Some parameters have to be parsed early so we can initialize stdout and the "host API".
   while (++argpos < argc && !initialparsefail)