Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -788,13 +788,10 @@
 	[AC_DEFINE(OF_HAVE_INTTYPES_H, 1, [Whether we have inttypes.h])])
 
 AC_CHECK_HEADER(sys/types.h,
 	[AC_DEFINE(OF_HAVE_SYS_TYPES_H, 1, [Whether we have sys/types.h])])
 
-AC_CHECK_TYPE(max_align_t,
-	[AC_DEFINE(OF_HAVE_MAX_ALIGN_T, 1, [Whether we have max_align_t])])
-
 AC_CHECK_HEADER(stdnoreturn.h,
 	[AC_DEFINE(OF_HAVE_STDNORETURN_H, 1, [Whether we have stdnoreturn.h])])
 
 AC_CHECK_TYPE(wchar_t)
 AC_CHECK_HEADER(wchar.h)

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -85,12 +85,12 @@
 #if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 	OFSpinlock retainCountSpinlock;
 #endif
 };
 
-#define PRE_IVARS_ALIGN ((sizeof(struct PreIvars) + \
-    (OF_BIGGEST_ALIGNMENT - 1)) & ~(OF_BIGGEST_ALIGNMENT - 1))
+#define PRE_IVARS_ALIGN \
+	OFRoundUpToPowerOf2(sizeof(struct PreIvars), OF_BIGGEST_ALIGNMENT)
 #define PRE_IVARS ((struct PreIvars *)(void *)((char *)self - PRE_IVARS_ALIGN))
 
 static struct {
 	Class isa;
 } allocFailedException;
@@ -338,12 +338,19 @@
 	if OF_UNLIKELY (extraAlignment > 1)
 		extraAlignment = OFRoundUpToPowerOf2(extraAlignment,
 		    PRE_IVARS_ALIGN + instanceSize) -
 		    PRE_IVARS_ALIGN - instanceSize;
 
+#ifndef OF_WINDOWS
 	instance = calloc(1, PRE_IVARS_ALIGN + instanceSize +
 	    extraAlignment + extraSize);
+#else
+	instance = _aligned_malloc(PRE_IVARS_ALIGN + instanceSize +
+	    extraAlignment + extraSize, OF_BIGGEST_ALIGNMENT);
+	memset(instance, 0, PRE_IVARS_ALIGN + instanceSize + extraAlignment +
+	    extraSize);
+#endif
 
 	if OF_UNLIKELY (instance == nil) {
 		object_setClass((id)&allocFailedException,
 		    [OFAllocFailedException class]);
 		@throw (id)&allocFailedException;
@@ -352,11 +359,15 @@
 	((struct PreIvars *)instance)->retainCount = 1;
 
 #if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 	if OF_UNLIKELY (OFSpinlockNew(
 	    &((struct PreIvars *)instance)->retainCountSpinlock) != 0) {
+# ifndef OF_WINDOWS
 		free(instance);
+# else
+		_aligned_free(instance);
+# endif
 		@throw [OFInitializationFailedException
 		    exceptionWithClass: class];
 	}
 #endif
 
@@ -365,11 +376,15 @@
 	if (!objc_constructInstance(class, instance)) {
 #if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 		OFSpinlockFree(&((struct PreIvars *)(void *)
 		    ((char *)instance - PRE_IVARS_ALIGN))->retainCountSpinlock);
 #endif
+#ifndef OF_WINDOWS
 		free((char *)instance - PRE_IVARS_ALIGN);
+#else
+		_aligned_free((char *)instance - PRE_IVARS_ALIGN);
+#endif
 		@throw [OFInitializationFailedException
 		    exceptionWithClass: class];
 	}
 
 	if OF_UNLIKELY (extra != NULL)
@@ -1232,11 +1247,15 @@
 
 #if !defined(OF_HAVE_ATOMIC_OPS) && !defined(OF_AMIGAOS)
 	OFSpinlockFree(&PRE_IVARS->retainCountSpinlock);
 #endif
 
+#ifndef OF_WINDOWS
 	free((char *)self - PRE_IVARS_ALIGN);
+#else
+	_aligned_free((char *)self - PRE_IVARS_ALIGN);
+#endif
 }
 
 /* Required to use properties with the Apple runtime */
 - (id)copyWithZone: (void *)zone
 {

Index: src/macros.h
==================================================================
--- src/macros.h
+++ src/macros.h
@@ -112,19 +112,23 @@
 #else
 # define OF_ALIGNOF(type) __alignof__(type)
 # define OF_ALIGNAS(type) OF_ALIGN(OF_ALIGNOF(type))
 #endif
 
-#if __STDC_VERSION__ >= 201112L && defined(OF_HAVE_MAX_ALIGN_T)
-# define OF_BIGGEST_ALIGNMENT _Alignof(max_align_t)
+#ifdef __BIGGEST_ALIGNMENT__
+# define OF_BIGGEST_ALIGNMENT __BIGGEST_ALIGNMENT__
 #else
-# ifdef __BIGGEST_ALIGNMENT__
-#  define OF_BIGGEST_ALIGNMENT __BIGGEST_ALIGNMENT__
-# else
-#  /* Hopefully no arch needs more than 16 byte alignment */
-#  define OF_BIGGEST_ALIGNMENT 16
-# endif
+/* Hopefully no arch needs more than 16 byte alignment */
+# define OF_BIGGEST_ALIGNMENT 16
+#endif
+/*
+ * We use SSE inline assembly on AMD64 and x86, so it must never be smaller
+ * than 16.
+ */
+#if (defined(OF_AMD64) || defined(OF_X86)) && OF_BIGGEST_ALIGNMENT < 16
+# undef OF_BIGGEST_ALIGNMENT
+# define OF_BIGGEST_ALIGNMENT 16
 #endif
 
 #define OF_PREPROCESSOR_CONCAT2(a, b) a##b
 #define OF_PREPROCESSOR_CONCAT(a, b) OF_PREPROCESSOR_CONCAT2(a, b)
 

Index: src/objfw-defs.h.in
==================================================================
--- src/objfw-defs.h.in
+++ src/objfw-defs.h.in
@@ -15,11 +15,10 @@
 #undef OF_HAVE_FORWARDING_TARGET_FOR_SELECTOR
 #undef OF_HAVE_IPV6
 #undef OF_HAVE_IPX
 #undef OF_HAVE_LIMITS_H
 #undef OF_HAVE_LINK
-#undef OF_HAVE_MAX_ALIGN_T
 #undef OF_HAVE_NETATALK_AT_H
 #undef OF_HAVE_NETAT_APPLETALK_H
 #undef OF_HAVE_NETINET_IN_H
 #undef OF_HAVE_NETINET_TCP_H
 #undef OF_HAVE_NETIPX_IPX_H