diff --git a/SConstruct b/SConstruct
index 6fe96b402..f736e3ae5 100644
--- a/SConstruct
+++ b/SConstruct
@@ -817,8 +817,11 @@ static void a(){{
 		raise SCons.Errors.StopError("Compiler cannot handle tuples of 2 elements.")
 	@_implicit_test
 	def check_poison_valgrind(self,context):
-		context.Display('%s: checking %s...' % (self.msgprefix, 'whether to use Valgrind poisoning'))
-		r = self.user_settings.poison == 'valgrind'
+		'''
+help:add Valgrind annotations; wipe certain freed memory when running under Valgrind
+'''
+		context.Message('%s: checking %s...' % (self.msgprefix, 'whether to use Valgrind poisoning'))
+		r = 'valgrind' in self.user_settings.poison
 		context.Result(r)
 		if not r:
 			return
@@ -831,9 +834,27 @@ static void a(){{
 		if self.Compile(context, text=text, main=main, msg='whether Valgrind memcheck header works', successflags={'CPPDEFINES' : ['DXX_HAVE_POISON_VALGRIND']}):
 			return True
 		raise SCons.Errors.StopError("Valgrind poison requested, but <valgrind/memcheck.h> does not work.")
+	@_implicit_test
+	def check_poison_overwrite(self,context):
+		'''
+help:always wipe certain freed memory
+'''
+		context.Message('%s: checking %s...' % (self.msgprefix, 'whether to use overwrite poisoning'))
+		r = 'overwrite' in self.user_settings.poison
+		context.Result(r)
+		if r:
+			context.sconf.Define('DXX_HAVE_POISON_OVERWRITE')
+		return r
 	@_custom_test
 	def _check_poison_method(self,context):
-		if self.check_poison_valgrind(context):
+		poison = None
+		for f in (
+			self.check_poison_valgrind,
+			self.check_poison_overwrite,
+		):
+			if f(context):
+				poison = True
+		if poison:
 			context.sconf.Define('DXX_HAVE_POISON')
 
 class LazyObjectConstructor:
@@ -1029,7 +1050,12 @@ class DXXCommon(LazyObjectConstructor):
 				'variable': self._enum_variable,
 				'arguments': (
 					('host_platform', 'linux' if sys.platform == 'linux2' else sys.platform, 'cross-compile to specified platform', {'allowed_values' : ['win32', 'darwin', 'linux']}),
-					('poison', 'none', 'method for poisoning free memory', {'allowed_values' : ('none', 'valgrind')}),
+				),
+			},
+			{
+				'variable': ListVariable,
+				'arguments': (
+					('poison', 'none', 'method for poisoning free memory', {'names' : ('valgrind', 'overwrite')}),
 				),
 			},
 			{
diff --git a/common/include/poison.h b/common/include/poison.h
index 9b449cb94..9100b589f 100644
--- a/common/include/poison.h
+++ b/common/include/poison.h
@@ -16,7 +16,8 @@ static inline void DXX_MAKE_MEM_UNDEFINED(T *b, unsigned long l)
 template <typename T>
 static inline void DXX_MAKE_MEM_UNDEFINED(T *b, T *e)
 {
-	DXX_MAKE_MEM_UNDEFINED(b, e - b);
+	unsigned char *bc = reinterpret_cast<unsigned char *>(b);
+	DXX_MAKE_MEM_UNDEFINED(bc, reinterpret_cast<unsigned char *>(e) - bc);
 }
 
 template <typename T, typename V>
@@ -24,8 +25,12 @@ static inline void _DXX_POISON_MEMORY_RANGE(T b, T e, const V &v)
 {
 #ifdef DXX_HAVE_POISON
 	int store = 0;
+#ifdef DXX_HAVE_POISON_OVERWRITE
+	store |= 1;
+#endif
 #ifdef DXX_HAVE_POISON_VALGRIND
-	store |= RUNNING_ON_VALGRIND;
+	if (!store)
+		store |= RUNNING_ON_VALGRIND;
 #endif
 	if (!store)
 		return;
diff --git a/similar/main/object.cpp b/similar/main/object.cpp
index ae2e4bb64..f8e1aa9e8 100644
--- a/similar/main/object.cpp
+++ b/similar/main/object.cpp
@@ -83,6 +83,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #include "compiler-range_for.h"
 #include "highest_valid.h"
 #include "partial_range.h"
+#include "poison.h"
 
 using std::min;
 using std::max;
@@ -1109,6 +1110,8 @@ objptridx_t obj_create(object_type_t type, ubyte id,vsegptridx_t segnum,const vm
 	// Zero out object structure to keep weird bugs from happening
 	// in uninitialized fields.
 	*obj = {};
+	// Tell Valgrind to warn on any uninitialized fields.
+	DXX_MAKE_MEM_UNDEFINED(&*obj, sizeof(*obj));
 
 	obj->signature				= obj_get_signature();
 	obj->type 					= type;
@@ -1252,7 +1255,7 @@ void obj_delete(const vobjptridx_t obj)
 	obj_unlink(obj);
 
 	Assert(Objects[0].next != 0);
-
+	DXX_MAKE_MEM_UNDEFINED(&*obj, sizeof(*obj));
 	obj->type = OBJ_NONE;		//unused!
 	obj->signature = -1;