diff --git a/blake2.cpp b/blake2.cpp
index e80985d4..96dedfbc 100644
--- a/blake2.cpp
+++ b/blake2.cpp
@@ -1,6 +1,17 @@
-// blake2.cpp - written and placed in the public domain by Jeffrey Walton and Zooko
-//              Wilcox-O'Hearn. Based on Aumasson, Neves, Wilcox-O'Hearn and Winnerlein's
-//              reference BLAKE2 implementation at http://github.com/BLAKE2/BLAKE2.
+// blake2.cpp - written and placed in the public domain by Jeffrey Walton
+//              and Zooko Wilcox-O'Hearn. Based on Aumasson, Neves,
+//              Wilcox-O'Hearn and Winnerlein's reference BLAKE2
+//              implementation at http://github.com/BLAKE2/BLAKE2.
+//
+// The BLAKE2b and BLAKE2s numbers are consistent with the BLAKE2 team's
+// numbers. However, we have an Altivec/POWER7 implementation of BLAKE2s,
+// and a POWER8 implementation of BLAKE2b (BLAKE2 is missing them). The
+// Altivec/POWER7 code is about 2x faster than C++ when using GCC 5.0 or
+// above. The POWER8 code is about 2.5x faster than C++ when using GCC 5.0
+// or above. If you use GCC 4.0 (PowerMac) or GCC 4.8 (GCC Compile Farm)
+// then the PowerPC code will be slower than C++. Be sure to use GCC 5.0
+// or above for PowerPC builds or disable Altivec for BLAKE2b and BLAKE2s
+// if using the old compilers.
 
 #include "pch.h"
 #include "config.h"
@@ -15,6 +26,7 @@
 // #undef CRYPTOPP_SSE41_AVAILABLE
 // #undef CRYPTOPP_ARM_NEON_AVAILABLE
 // #undef CRYPTOPP_ALTIVEC_AVAILABLE
+// #undef CRYPTOPP_POWER8_AVAILABLE
 
 // Disable NEON/ASIMD for Cortex-A53 and A57. The shifts are too slow and C/C++ is about
 // 3 cpb faster than NEON/ASIMD. Also see http://github.com/weidai11/cryptopp/issues/367.
@@ -22,11 +34,6 @@
 # undef CRYPTOPP_ARM_NEON_AVAILABLE
 #endif
 
-#if !(CRYPTOPP_ALTIVEC_AVAILABLE)
-# undef CRYPTOPP_POWER7_AVAILABLE
-# undef CRYPTOPP_POWER8_AVAILABLE
-#endif
-
 NAMESPACE_BEGIN(CryptoPP)
 
 // Export the tables to the SIMD files
@@ -155,7 +162,7 @@ extern void BLAKE2_Compress32_NEON(const byte* input, BLAKE2s_State& state);
 extern void BLAKE2_Compress64_NEON(const byte* input, BLAKE2b_State& state);
 #endif
 
-#if CRYPTOPP_POWER7_AVAILABLE
+#if CRYPTOPP_ALTIVEC_AVAILABLE
 extern void BLAKE2_Compress32_POWER7(const byte* input, BLAKE2s_State& state);
 #endif
 
@@ -383,6 +390,10 @@ std::string BLAKE2s::AlgorithmProvider() const
 #if (CRYPTOPP_POWER7_AVAILABLE)
     if (HasPower7())
         return "Power7";
+#endif
+#if (CRYPTOPP_ALTIVEC_AVAILABLE)
+    if (HasAltivec())
+        return "Altivec";
 #endif
     return "C++";
 }
@@ -655,8 +666,8 @@ void BLAKE2s::Compress(const byte *input)
         return BLAKE2_Compress32_NEON(input, *m_state.data());
     }
 #endif
-#if CRYPTOPP_POWER7_AVAILABLE
-    if(HasPower7())
+#if CRYPTOPP_ALTIVEC_AVAILABLE
+    if(HasAltivec())
     {
         return BLAKE2_Compress32_POWER7(input, *m_state.data());
     }
diff --git a/blake2.h b/blake2.h
index 1a999036..a34d9285 100644
--- a/blake2.h
+++ b/blake2.h
@@ -1,6 +1,7 @@
-// blake2.h - written and placed in the public domain by Jeffrey Walton and Zooko
-//            Wilcox-O'Hearn. Based on Aumasson, Neves, Wilcox-O'Hearn and Winnerlein's
-//            reference BLAKE2 implementation at http://github.com/BLAKE2/BLAKE2.
+// blake2.h - written and placed in the public domain by Jeffrey Walton
+//            and Zooko Wilcox-O'Hearn. Based on Aumasson, Neves,
+//            Wilcox-O'Hearn and Winnerlein's reference BLAKE2
+//            implementation at http://github.com/BLAKE2/BLAKE2.
 
 /// \file blake2.h
 /// \brief Classes for BLAKE2b and BLAKE2s message digests and keyed message digests
diff --git a/blake2s_simd.cpp b/blake2s_simd.cpp
index 45e0043e..cc1ec137 100644
--- a/blake2s_simd.cpp
+++ b/blake2s_simd.cpp
@@ -7,6 +7,16 @@
 //    needed because additional CXXFLAGS are required to enable the
 //    appropriate instructions sets in some build configurations.
 
+// The BLAKE2b and BLAKE2s numbers are consistent with the BLAKE2 team's
+// numbers. However, we have an Altivec/POWER7 implementation of BLAKE2s,
+// and a POWER8 implementation of BLAKE2b (BLAKE2 is missing them). The
+// Altivec/POWER7 code is about 2x faster than C++ when using GCC 5.0 or
+// above. The POWER8 code is about 2.5x faster than C++ when using GCC 5.0
+// or above. If you use GCC 4.0 (PowerMac) or GCC 4.8 (GCC Compile Farm)
+// then the PowerPC code will be slower than C++. Be sure to use GCC 5.0
+// or above for PowerPC builds or disable Altivec for BLAKE2b and BLAKE2s
+// if using the old compilers.
+
 #include "pch.h"
 #include "config.h"
 #include "misc.h"
@@ -41,7 +51,7 @@
 # include <arm_acle.h>
 #endif
 
-#if (CRYPTOPP_POWER7_AVAILABLE)
+#if (CRYPTOPP_ALTIVEC_AVAILABLE)
 # include "ppc_simd.h"
 #endif
 
@@ -671,7 +681,7 @@ void BLAKE2_Compress32_NEON(const byte* input, BLAKE2s_State& state)
 }
 #endif  // CRYPTOPP_ARM_NEON_AVAILABLE
 
-#if (CRYPTOPP_POWER7_AVAILABLE)
+#if (CRYPTOPP_ALTIVEC_AVAILABLE)
 
 inline uint32x4_p VectorLoad32(const void* p)
 {
@@ -984,6 +994,6 @@ void BLAKE2_Compress32_POWER7(const byte* input, BLAKE2s_State& state)
     VectorStore32LE(&state.h[0], vec_xor(ff0, vec_xor(row1, row3)));
     VectorStore32LE(&state.h[4], vec_xor(ff1, vec_xor(row2, row4)));
 }
-#endif  // CRYPTOPP_POWER7_AVAILABLE
+#endif  // CRYPTOPP_ALTIVEC_AVAILABLE
 
 NAMESPACE_END