Index: src/OFMatrix4x4.h
==================================================================
--- src/OFMatrix4x4.h
+++ src/OFMatrix4x4.h
@@ -91,13 +91,18 @@
  */
 - (OFVector4D)transformedVector: (OFVector4D)vector;
 
 /**
  * @brief Transforms the specified vectors in-place according to the matrix.
+ *
+ * @warning Please note that the vectors must be 16 byte aligned! This is
+ *	    required to allow SIMD optimizations. Passing a pointer to vectors
+ *	    that are not 16 byte aligned will crash if SIMD optimizations are
+ *	    enabled.
  *
  * @param vectors The vectors to transform
  * @param count The count of the specified vectors
  */
 - (void)transformVectors: (OFVector4D *)vectors count: (size_t)count;
 @end
 
 OF_ASSUME_NONNULL_END

Index: src/OFMatrix4x4.m
==================================================================
--- src/OFMatrix4x4.m
+++ src/OFMatrix4x4.m
@@ -362,11 +362,11 @@
 	[scale release];
 }
 
 - (OFVector4D)transformedVector: (OFVector4D)vector
 {
-	OFVector4D copy = vector;
+	OF_ALIGN(16) OFVector4D copy = vector;
 
 	[self transformVectors: &copy count: 1];
 
 	return copy;
 }

Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -347,11 +347,11 @@
 /**
  * @struct OFVector4D OFObject.h ObjFW/OFObject.h
  *
  * @brief A vector in 4D space.
  */
-typedef struct OF_ALIGN(16) OF_BOXABLE OFVector4D {
+typedef struct OF_BOXABLE OFVector4D {
 	/** The x coordinate of the vector */
 	float x;
 	/** The y coordinate of the vector */
 	float y;
 	/** The z coordinate of the vector */

Index: src/macros.h
==================================================================
--- src/macros.h
+++ src/macros.h
@@ -100,18 +100,16 @@
 # define OF_CONST_FUNC
 # define OF_NO_RETURN_FUNC
 # define OF_WEAK_REF(sym)
 #endif
 
-#ifdef __GNUC__
-# define OF_ALIGN(alignment) __attribute__((__aligned__(alignment)))
-#endif
-
 #if __STDC_VERSION__ >= 201112L
+# define OF_ALIGN(size) _Alignas(size)
 # define OF_ALIGNOF(type) _Alignof(type)
 # define OF_ALIGNAS(type) _Alignas(type)
 #else
+# define OF_ALIGN(size) __attribute__((__aligned__(size)))
 # define OF_ALIGNOF(type) __alignof__(type)
 # define OF_ALIGNAS(type) OF_ALIGN(OF_ALIGNOF(type))
 #endif
 
 #ifdef __BIGGEST_ALIGNMENT__

Index: tests/OFMatrix4x4Tests.m
==================================================================
--- tests/OFMatrix4x4Tests.m
+++ tests/OFMatrix4x4Tests.m
@@ -147,11 +147,11 @@
 	OTAssertEqual(point.w, 1);
 }
 
 - (void)testTransformVectorsCount
 {
-	OFVector4D points[2] = {{ 1, 2, 3, 1 }, { 7, 8, 9, 2 }};
+	OF_ALIGN(16) OFVector4D points[2] = {{ 1, 2, 3, 1 }, { 7, 8, 9, 2 }};
 
 	[_matrix transformVectors: points count: 2];
 
 	OTAssertEqual(points[0].x, 18);
 	OTAssertEqual(points[0].y, 46);