diff --git a/CMakeLists.txt b/CMakeLists.txt
index fa26069c..0691adcd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -103,6 +103,11 @@ endif()
 set(SHELL_CMD sh -c)
 set(GREP_CMD egrep -i -c)
 
+execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
+	COMMAND ${GREP_CMD} "amd64"
+	OUTPUT_VARIABLE CRYPTOPP_AMD64
+	OUTPUT_STRIP_TRAILING_WHITESPACE)
+
 execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
 	COMMAND ${GREP_CMD} "x86_64"
 	OUTPUT_VARIABLE CRYPTOPP_X86_64
@@ -144,6 +149,10 @@ execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
 	OUTPUT_VARIABLE CRYPTOPP_ARM7L
 	OUTPUT_STRIP_TRAILING_WHITESPACE)
 
+# OpenBSD and Clang
+if ("${CRYPTOPP_X86_64}" STREQUAL "1")
+	set(CRYPTOPP_AMD64 "1")
+endif()
 # arm7l is another 32-bit hard float machine. RPI-3 is arm7l on 64-bit hardware
 if ("${CRYPTOPP_ARM}" STREQUAL "1")
 	set(CRYPTOPP_ARMHF "1")
@@ -367,7 +376,7 @@ endif()
 # New as of Pull Request 461, http://github.com/weidai11/cryptopp/pull/461.
 if (("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang") OR ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU"))
 
-	if (("${CRYPTOPP_X86_64}" STREQUAL "1") OR ("${CRYPTOPP_I386}" STREQUAL "1") OR ("${CRYPTOPP_X32}" STREQUAL "1"))
+	if (("${CRYPTOPP_AMD64}" STREQUAL "1") OR ("${CRYPTOPP_I386}" STREQUAL "1") OR ("${CRYPTOPP_X32}" STREQUAL "1"))
 
 		CHECK_CXX_COMPILER_FLAG("-mssse3" CRYPTOPP_IA32_SSSE3)
 		CHECK_CXX_COMPILER_FLAG("-msse4.2" CRYPTOPP_IA32_SSE4)
diff --git a/GNUmakefile b/GNUmakefile
old mode 100755
new mode 100644