diff --git a/rijndael-simd.cpp b/rijndael-simd.cpp
index de5df3e0..4ed94012 100644
--- a/rijndael-simd.cpp
+++ b/rijndael-simd.cpp
@@ -10,6 +10,9 @@
 //    Skip Hovsmith and Barry O'Rourke for the mbedTLS project. Stepping
 //    mbedTLS under a debugger was helped for us to determine problems
 //    with our subkey generation and scheduling.
+//
+//    AltiVec and Power8 code based on "POWER8 in-core cryptography."
+//    http://www.ibm.com/developerworks/library/se-power8-in-core-cryptography/index.html
 
 #include "pch.h"
 #include "config.h"
@@ -24,7 +27,7 @@
 // Hack... We are supposed to use <nmmintrin.h>. GCC 4.8, LLVM Clang 3.5
 //   and Apple Clang 6.0 conflates SSE4.1 and SSE4.2. If we use <nmmintrin.h>
 //   then compile fails with "SSE4.2 instruction set not enabled". Also see
-//   https://gcc.gnu.org/ml/gcc-help/2017-08/msg00015.html.
+//   http://gcc.gnu.org/ml/gcc-help/2017-08/msg00015.html.
 # include "smmintrin.h"
 # include "wmmintrin.h"
 #endif
diff --git a/rijndael.cpp b/rijndael.cpp
index 3c2a2cad..5a354cfa 100644
--- a/rijndael.cpp
+++ b/rijndael.cpp
@@ -220,6 +220,15 @@ void Rijndael::Base::FillDecTable()
 	s_TdFilled = true;
 }
 
+unsigned int Rijndael::Base::OptimalDataAlignment() const
+{
+#if CRYPTOPP_BOOL_ALIGN16
+	return 16;
+#else
+	return GetAlignmentOf<word32>();
+#endif
+}
+
 #if (CRYPTOPP_AESNI_AVAILABLE)
 extern void Rijndael_UncheckedSetKey_SSE4_AESNI(const byte *userKey, size_t keyLen, word32* rk);
 extern void Rijndael_UncheckedSetKeyRev_AESNI(word32 *key, unsigned int rounds);
diff --git a/rijndael.h b/rijndael.h
index 483eab5a..2a1c44e8 100644
--- a/rijndael.h
+++ b/rijndael.h
@@ -39,6 +39,9 @@ class CRYPTOPP_DLL Rijndael : public Rijndael_Info, public BlockCipherDocumentat
 	class CRYPTOPP_DLL CRYPTOPP_NO_VTABLE Base : public BlockCipherImpl<Rijndael_Info>
 	{
 	public:
+		// Intel and ARM SIMD units can handle unaligned loads, but AltiVec and Power8 cannot.
+		unsigned int OptimalDataAlignment() const;
+
 		void UncheckedSetKey(const byte *userKey, unsigned int keyLength, const NameValuePairs &params);
 
 	protected: