diff --git a/luprex/core/Makefile b/luprex/core/Makefile
index 6171b3a2..c8c082de 100644
--- a/luprex/core/Makefile
+++ b/luprex/core/Makefile
@@ -1,15 +1,26 @@
-OS=unspecified
+
 
 ifeq ($(OS),mingw)
   EXE=main.exe
   LIBS=-lws2_32
   LUAFLAGS=-DLUA_COMPAT_ALL
+  OPT=-g -O1
+  DRIVER=driver-mingw
 else ifeq ($(OS),linux)
   EXE=main
   LIBS=
   LUAFLAGS=-DLUA_USE_POSIX
+  OPT=-g -O1
+  DRIVER=driver-linux
 else
-  $(error You must specify OS=linux or OS=mingw)
+  # In this case, any attempt to build luprex will trigger an error,
+  # But making 'clean' will still work.
+  ERROR=$(error You must specify OS=linux or OS=mingw)
+  EXE=main
+  LIBS=$(ERROR)
+  LUAFLAGS=$(ERROR)
+  OPT=$(ERROR)
+  DRIVER=driver-xxx
 endif
 
 LUA_OBJ_FILES=\
@@ -80,18 +91,18 @@ CORE_OBJ_FILES=\
 	obj/drivertests.o\
 	obj/printbuffer.o\
 	obj/main.o \
-	obj/driver-$(OS).o\
+	obj/$(DRIVER).o\
 
 
 lobj/%.o: ../eris-master/src/%.c
-	gcc -Wall -g -DLUA_USE_APICHECK $(LUAFLAGS) -c -MMD $< -o $@
+	gcc -Wall $(OPT) -DLUA_USE_APICHECK $(LUAFLAGS) -c -MMD $< -o $@
 
 obj/%.o: cpp/%.cpp
-	g++ -std=c++17 -Wall -g -Iinc -Icpp -c -MMD $< -o $@
+	g++ -std=c++17 -Wall $(OPT) -Iinc -Icpp -c -MMD $< -o $@
 
 
 $(EXE): $(CORE_OBJ_FILES) $(LUA_OBJ_FILES)
-	g++ -std=c++17 -Wall -g -o $@ $(CORE_OBJ_FILES) $(LUA_OBJ_FILES) $(LIBS)
+	g++ -std=c++17 -Wall $(OPT) -o $@ $(CORE_OBJ_FILES) $(LUA_OBJ_FILES) $(LIBS)
 
 clean:
 	rm -f main.exe main obj/* lobj/*
diff --git a/luprex/core/cpp/streambuffer.cpp b/luprex/core/cpp/streambuffer.cpp
index e7730add..8e9313c8 100644
--- a/luprex/core/cpp/streambuffer.cpp
+++ b/luprex/core/cpp/streambuffer.cpp
@@ -107,7 +107,7 @@ char *StreamBuffer::get_overwrite(int64_t size, int64_t write_count_after) {
 void StreamBuffer::clear() {
     assert(owned_);
     if (!fixed_size_) {
-        if (buf_lo_ != nullptr) delete buf_lo_;
+        if (buf_lo_ != nullptr) free(buf_lo_);
         buf_lo_ = 0;
         buf_hi_ = 0;
     }