diff --git a/Docs/src/history.but b/Docs/src/history.but
index 27888b16..184d42b9 100644
--- a/Docs/src/history.but
+++ b/Docs/src/history.but
@@ -36,6 +36,8 @@ Released on ? ?th, 2020
 
 \S2{} Build System
 
+\b Primitive SOURCE_DATE_EPOCH support (\W{http://sf.net/p/nsis/patches/294}{patch #294})
+
 \b Python 3 fixes (\W{http://sf.net/p/nsis/patches/296}{patch #296})
 
 \H{v3.05} 3.05
diff --git a/SCons/Config/gnu b/SCons/Config/gnu
index bfcb362d..1e6b509e 100644
--- a/SCons/Config/gnu
+++ b/SCons/Config/gnu
@@ -4,13 +4,13 @@ Import('defenv')
 
 ### imports
 
-Import('FlagsConfigure GetOptionOrEnv')
+Import('FlagsConfigure GetOptionOrEnv GetStdSysEnvVarList')
 
 ### HACKS!
 if GetOptionOrEnv('NSIS_SCONS_GNU_ENVPATHHACK'):
 	import os
 	defenv['ENV']['PATH'] = os.getenv('PATH') # Major hack!
-	import_env = ['SystemDrive', 'SystemRoot', 'TEMP', 'TMP', 'PATHEXT']
+	import_env = GetStdSysEnvVarList(path=True, temp=True)
 	for var in import_env: 
 		if var in os.environ:
 			defenv['ENV'][var] = os.environ.get(var, '')
diff --git a/SCons/Tools/mstoolkit.py b/SCons/Tools/mstoolkit.py
index 1edbb7a4..42d3ed20 100644
--- a/SCons/Tools/mstoolkit.py
+++ b/SCons/Tools/mstoolkit.py
@@ -290,7 +290,7 @@ def generate(env):
 	targ_arc = env.get('TARGET_ARCH', 'x86')
 
 	if "None" == env.get('MSVC_USE_SCRIPT', '!'):
-		for x in ['INCLUDE', 'LIB', 'PATH', 'CL', 'LINK', 'ML']: env['ENV'][x] = ""
+		for x in ['INCLUDE', 'LIB', 'PATH', 'CL', '_CL_', 'LINK', '_LINK_', 'ML']: env['ENV'][x] = ""
 		if not env.WhereIs('cl', os.environ['PATH']):
 			raise SCons.Errors.InternalError("CL not found in %s" % os.environ['PATH'])
 		include_path = os.environ['INCLUDE']
@@ -312,6 +312,7 @@ def generate(env):
 	env.PrependENVPath('INCLUDE', include_path)
 	env.PrependENVPath('LIB', lib_path)
 	env.PrependENVPath('PATH', exe_path)
+	# 'LIBPATH' = ?
 
 	env['ENV']['CPU'] = (targ_arc.upper(), 'i386')['x86' in targ_arc.lower()] # AMD64/ARM64 or i386
 	env['ENV']['TARGETOS'] = 'BOTH'
diff --git a/SCons/utils.py b/SCons/utils.py
index 0b5315e9..92d50ceb 100644
--- a/SCons/utils.py
+++ b/SCons/utils.py
@@ -1,3 +1,31 @@
+def IsExecutingOnWindows():
+	import sys, os
+	if sys.platform.startswith('win') or os.name == 'nt': return True
+	return False
+
+def GetWindowsStdSysEnvVarList(path=False, temp=True, user=True, os=True, shell=True, cpu=True):
+	ret = []
+	if os: ret += 'OS WINDIR SYSTEMDRIVE SYSTEMROOT ALLUSERSPROFILE Public ProgramData CommonProgramFiles CommonProgramFiles(x86) CommonProgramW6432 ProgramFiles ProgramFiles(x86) ProgramW6432'.split()
+	if cpu: ret += 'NUMBER_OF_PROCESSORS PROCESSOR_ARCHITECTURE PROCESSOR_ARCHITEW6432 PROCESSOR_IDENTIFIER PROCESSOR_LEVEL PROCESSOR_REVISION'.split()
+	if user: ret += 'COMPUTERNAME USERNAME USERPROFILE APPDATA LOCALAPPDATA HOMEDRIVE HOMESHARE HOMEPATH LOGONSERVER USERDNSDOMAIN USERDOMAIN USERDOMAIN_ROAMINGPROFILE ClientName SessionName'.split()
+	if shell: ret += 'COMSPEC PATHEXT PSModulePath'.split() # PROMPT
+	if temp: ret += 'TEMP TMP'.split()
+	if path: ret += 'PATH'.split()
+	return ret
+def GetPosixStdSysEnvVarList(path=False, temp=True, user=True, os=True, shell=True, cpu=True):
+	ret = []
+	if os: ret += 'HOSTALIASES'.split()
+	if user: ret += 'HOME USER LOGNAME DATEMSK UID'.split() # XDG_* TZ LANGUAGE LANG LC_* NLSPATH
+	if shell: ret += 'SHELL TERM TERMCAP'.split()
+	if temp: ret += 'TMPDIR'.split()
+	if path: ret += 'PATH MANPATH'.split()
+	return ret
+def GetStdSysEnvVarList(path=False, temp=True, user=True, os=True, shell=True, cpu=True):
+	func = GetPosixStdSysEnvVarList
+	if IsExecutingOnWindows(): func = GetWindowsStdSysEnvVarList
+	return func(path=path, temp=temp, user=user, os=os, shell=shell, cpu=cpu)
+
+
 def AddAvailableLibs(env, libs):
 	"""
 	Scans through a list of libraries and adds
@@ -145,10 +173,10 @@ def ReadU32LE(f, fpos=None, defval=None):
 	return FileUnpackRead("<I", 4, f, fpos, defval)
 def WriteU16LE(f, v, fpos):
 	if not fpos is None: f.seek(fpos)
-	f.write(struct.pack("<H", v))
+	return f.write(struct.pack("<H", v))
 def WriteU32LE(f, v, fpos):
 	if not fpos is None: f.seek(fpos)
-	f.write(struct.pack("<I", v))
+	return f.write(struct.pack("<I", v))
 
 class MSPE:
 	def __init__(self, path=None, open_for_write=False):
@@ -177,16 +205,24 @@ class MSPE:
 		self.IsPEP = 0x20b == self.NTOHMagic # IMAGE_NT_OPTIONAL_HDR64_MAGIC?
 	def ReadMachine(self):
 		return ReadU16LE(self._f, self.NTHOffset+4+0)
+	def WriteTimeDateStamp(self, value):
+		return WriteU32LE(self._f, value, self.NTHOffset+4+4)
 	def ReadCharacteristics(self):
 		return ReadU16LE(self._f, self.NTHOffset+4+18)
 	def WriteCharacteristics(self, value):
-		WriteU16LE(self._f, value, self.NTHOffset+4+18)
+		return WriteU16LE(self._f, value, self.NTHOffset+4+18)
 	def ReadDllCharacteristics(self):
 		return ReadU16LE(self._f, self.NTHOffset+4+20+70)
 	def WriteDllCharacteristics(self, value):
-		WriteU16LE(self._f, value, self.NTHOffset+4+20+70)
+		return WriteU16LE(self._f, value, self.NTHOffset+4+20+70)
 	def WriteChecksum(self, value):
-		WriteU32LE(self._f, value, self.NTHOffset+4+20+64)
+		return WriteU32LE(self._f, value, self.NTHOffset+4+20+64)
+	def InvalidateChecksum(self):
+		return self.WriteChecksum(0) and 0
+
+def IsPE(pe):
+	if not isinstance(pe, MSPE): pe = MSPE(pe)
+	if not pe.NTOHMagic is None: return True
 
 def IsPEExecutable(pe):
 	if not isinstance(pe, MSPE): pe = MSPE(pe)
@@ -211,8 +247,25 @@ def SetPESecurityFlagsWorker(filepath):
 			ioh_dc |= 0x0040 # +IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE (ASLR)
 			if pe.IsPEP: ioh_dc |= 0x0020 # +IMAGE_DLLCHARACTERISTICS_HIGH_ENTROPY_VA (HEASLR)
 		pe.WriteDllCharacteristics(ioh_dc)
-		pe.WriteChecksum(0)
+		pe.InvalidateChecksum()
 	finally:
 		return
 
-Export('AddAvailableLibs AddZLib FlagsConfigure GetAvailableLibs GetOptionOrEnv IsPEExecutable SetPESecurityFlagsWorker')
+def SetPETimestamp(filepath, timestamp):
+	pe = MSPE(filepath, open_for_write=True)
+	try:
+		if not IsPE(pe): return
+		pe.WriteTimeDateStamp(int(timestamp or 0))
+		pe.InvalidateChecksum()
+		return True
+	finally:
+		return
+
+def MakeReproducibleAction(target, source, env):
+	if env.get('SOURCE_DATE_EPOCH','') is not '':
+		SetPETimestamp(target[0].path, env['SOURCE_DATE_EPOCH'])
+
+def SilentActionEcho(target, source, env):
+	return None
+
+Export('GetStdSysEnvVarList AddAvailableLibs AddZLib FlagsConfigure GetAvailableLibs GetOptionOrEnv SilentActionEcho IsPEExecutable SetPESecurityFlagsWorker MakeReproducibleAction')
diff --git a/SConstruct b/SConstruct
index 53c2c045..e0026125 100644
--- a/SConstruct
+++ b/SConstruct
@@ -64,20 +64,20 @@ doctypes = [
 #######  Build Environment                                         ###
 ######################################################################
 
+import os
 path = ARGUMENTS.get('PATH', '')
 toolset = ARGUMENTS.get('TOOLSET', '')
-arch = ARGUMENTS.get('TARGET_ARCH', 'x86')
 
-if toolset and path:
-	defenv = Environment(TARGET_ARCH = arch, ENV = {'PATH' : path}, TOOLS = toolset.split(',') + ['zip'])
-else:
-	if path:
-		defenv = Environment(TARGET_ARCH = arch, ENV = {'PATH' : path})
-	if toolset:
-		defenv = Environment(TARGET_ARCH = arch, TOOLS = toolset.split(',') + ['zip'])
-if not toolset and not path:
-	defenv = Environment(TARGET_ARCH = arch)
+defenv = {
+	'TARGET_ARCH': ARGUMENTS.get('TARGET_ARCH', 'x86'),
+	'ENV': {}
+}
 
+if path: defenv['ENV']['PATH'] = path
+if toolset: defenv['TOOLS'] = toolset.split(',') + ['zip']
+
+if len(defenv['ENV']) == 0: del defenv['ENV']
+defenv = Environment(**defenv)
 Export('defenv')
 
 ######################################################################
@@ -85,12 +85,12 @@ Export('defenv')
 ######################################################################
 
 SConscript('SCons/utils.py')
+Import('GetOptionOrEnv')
 
 ######################################################################
 #######  Options                                                   ###
 ######################################################################
 
-import os
 default_doctype = 'html'
 if defenv.WhereIs('hhc', os.environ['PATH']):
 	default_doctype = 'chm'
@@ -195,6 +195,8 @@ opts.Add(('PREFIX_DATA', 'Path to install nsis data to (plugins, includes, stubs
 opts.Add(('PREFIX_DOC','Path to install nsis README / INSTALL / TODO files to.', dirs['doc']))
 opts.Add(('PREFIX_PLUGINAPI_INC','Path to install plugin API headers to.', None))
 opts.Add(('PREFIX_PLUGINAPI_LIB','Path to install plugin static library to.', None))
+# reproducible builds
+opts.Add(('SOURCE_DATE_EPOCH', 'UNIX timestamp (in seconds)', os.environ.get('SOURCE_DATE_EPOCH')))
 
 opts.Update(defenv)
 Help(opts.GenerateHelpText(defenv))
@@ -211,6 +213,10 @@ if 'NSIS_CONFIG_CONST_DATA_PATH' in defenv['NSIS_CPPDEFINES']:
 	defenv.Append(NSIS_CPPDEFINES = [('PREFIX_DATA', '"%s"' % defenv.subst('$PREFIX_DATA'))])
 	defenv.Append(NSIS_CPPDEFINES = [('PREFIX_DOC', '"%s"' % defenv.subst('$PREFIX_DOC'))])
 
+if defenv.get('SOURCE_DATE_EPOCH','') is not '':
+	defenv['ENV']['SOURCE_DATE_EPOCH'] = defenv['SOURCE_DATE_EPOCH'] = int(defenv['SOURCE_DATE_EPOCH'], 0) # Normalize and apply to ENV for child processes
+	defenv.Append(NSIS_CPPDEFINES = [('NSIS_SOURCE_DATE_EPOCH', '%s' % defenv['SOURCE_DATE_EPOCH'])]) # Display in /HDRINFO
+
 # Need this early for the config header files to be placed in
 if defenv['UNICODE']:
 	if defenv['DEBUG']:
@@ -441,7 +447,7 @@ def Sign(targets):
 			a = defenv.Action('$CODESIGNER "%s"' % t.path)
 			defenv.AddPostAction(t, a)
 
-Import('IsPEExecutable SetPESecurityFlagsWorker')
+Import('SilentActionEcho IsPEExecutable SetPESecurityFlagsWorker MakeReproducibleAction')
 def SetPESecurityFlagsAction(target, source, env):
 	for t in target:
 		SetPESecurityFlagsWorker(t.path)
@@ -454,6 +460,10 @@ def SetPESecurityFlags(targets):
 		a = defenv.Action(SetPESecurityFlagsAction, strfunction=SetPESecurityFlagsActionEcho)
 		defenv.AddPostAction(t, a)
 
+def MakeReproducible(targets):
+	for t in targets:
+		defenv.AddPostAction(t, defenv.Action(MakeReproducibleAction, strfunction=SilentActionEcho))
+
 def TestScript(scripts):
 	defenv.Install('$TESTDISTDIR/Tests', scripts)
 
@@ -471,6 +481,7 @@ defenv.DistributeDocs = DistributeDocs
 defenv.DistributeExamples = DistributeExamples
 defenv.Sign = Sign
 defenv.SetPESecurityFlags = SetPESecurityFlags
+defenv.MakeReproducible = MakeReproducible
 defenv.TestScript = TestScript
 
 def DistributeExtras(env, target, examples, docs):
@@ -484,7 +495,6 @@ def DistributeExtras(env, target, examples, docs):
 ######################################################################
 
 if defenv['MSTOOLKIT']:
-	Import('GetOptionOrEnv')
 	if GetOptionOrEnv('MSVC_USE_SCRIPT', '!') != '!':
 		defenv['MSVC_USE_SCRIPT'] = GetOptionOrEnv('MSVC_USE_SCRIPT')
 	defenv.Tool('mstoolkit', toolpath = [Dir('SCons/Tools').rdir()])
@@ -559,6 +569,7 @@ if defenv['PLATFORM'] == 'win32':
 	nsis_menu_target = defenv.Command(os.path.join('$ZIPDISTDIR', 'NSIS.exe'),
 																		os.path.join('$ZIPDISTDIR', 'Examples', 'NSISMenu.nsi'),
 																		build_nsis_menu_for_zip)
+	defenv.MakeReproducible(nsis_menu_target)
 	defenv.Sign(nsis_menu_target)
 
 dist_zip = 'nsis-${VERSION}${DISTSUFFIX}.zip'
@@ -641,6 +652,7 @@ def BuildStub(compression, solid, unicode):
 	target = defenv.SConscript(dirs = 'Source/exehead', variant_dir = build_dir, duplicate = False, exports = exports)
 	env.SideEffect('%s/stub_%s.map' % (build_dir, stub), target)
 
+	env.MakeReproducible(target)
 	env.DistributeStubs(target, names=compression+suffix)
 
 	defenv.Alias(compression, target)
@@ -672,6 +684,7 @@ makensis = defenv.SConscript(dirs = 'Source', variant_dir = build_dir, duplicate
 
 makensis_env.SideEffect('%s/makensis.map' % build_dir, makensis)
 
+defenv.MakeReproducible(makensis)
 defenv.Alias('makensis', makensis)
 
 if defenv['PLATFORM'] == 'win32': 
@@ -709,6 +722,7 @@ def BuildPluginWorker(target, source, libs, examples = None, docs = None,
 	defenv.Alias('plugins', plugin)
 
 	defenv.SetPESecurityFlags(plugin)
+	defenv.MakeReproducible(plugin)
 	defenv.Sign(plugin)
 
 	CleanMap(env, plugin, target)
@@ -803,6 +817,7 @@ def BuildUtil(target, source, libs, entry = None, res = None,
 	defenv.Alias(target, util)
 	defenv.Alias('utils', util)
 
+	defenv.MakeReproducible(util)
 	defenv.Sign(util)
 
 	CleanMap(env, util, target)
diff --git a/Source/build.cpp b/Source/build.cpp
index a34210d2..91fb989a 100644
--- a/Source/build.cpp
+++ b/Source/build.cpp
@@ -3624,7 +3624,7 @@ bool CEXEBuild::hostapi_request_data(MakensisAPI::datatransfer_e operation, UINT
       return data && ((HOSTAPIREQUESTDATAPROC)data[0])((void*) data[1], hWnd, Msg, wParam, lParam); // We don't set DWLP_MSGRESULT nor care about the return value
     }
   };
-  if (!notify_hwnd || (minver && SendMessage(notify_hwnd, QUERYHOST, QH_SUPPORTEDVERSION, 0) < minver)) return false;
+  if (!notify_hwnd || (minver && (UINT) SendMessage(notify_hwnd, QUERYHOST, QH_SUPPORTEDVERSION, 0) < minver)) return false;
   size_t data[] = { (size_t) proc, (size_t) cookie };
   COPYDATASTRUCT cds = { (DWORD) operation, inputsize, (void*) input };
   HWND hWnd = CreateWindowEx(WS_EX_TOOLWINDOW, WC_DIALOG, NULL, WS_POPUP|WS_DISABLED, 0, 0, 0, 0, NULL, NULL, NULL, NULL);