diff --git a/.travis.yml b/.travis.yml
index 1ef8d774..e29d99b0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,6 +23,7 @@ env:
 
   matrix:
     - BUILD_MODE="all"
+    - BUILD_MODE="native"
     - BUILD_MODE="no-asm"
     - BUILD_MODE="debug"
     - BUILD_MODE="asan"
@@ -55,6 +56,9 @@ matrix:
       env: BUILD_MODE="ios-watch"
     - os: linux
       env: BUILD_MODE="ios-tv"
+    # No Native builds on iOS
+    - os: osx
+      env: BUILD_MODE="native"
 
   allow_failures:
     - os: osx
diff --git a/GNUmakefile b/GNUmakefile
old mode 100644
new mode 100755
index ebfdfcba..c14d540a
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -123,7 +123,7 @@ endif
 
 ifneq ($(HAS_NEWLIB),0)
  ifeq ($(findstring -D_XOPEN_SOURCE,$(CXXFLAGS)),)
-   CXXFLAGS += -D_XOPEN_SOURCE=700
+   CXXFLAGS += -D_XOPEN_SOURCE=600
  endif
 endif
 
@@ -403,6 +403,13 @@ CXXFLAGS += -DCRYPTOPP_DISABLE_ASM
 endif # CXXFLAGS
 endif # No ASM
 
+# Native build testing. Issue 'make native'.
+ifeq ($(findstring native,$(MAKECMDGOALS)),native)
+ifeq ($(findstring -march=native,$(CXXFLAGS)),)
+CXXFLAGS += -march=native
+endif # CXXFLAGS
+endif # Native
+
 # Undefined Behavior Sanitizer (UBsan) testing. Issue 'make ubsan'.
 ifeq ($(findstring ubsan,$(MAKECMDGOALS)),ubsan)
 CXXFLAGS := $(CXXFLAGS:-g%=-g3)
@@ -593,8 +600,8 @@ dep deps depend GNUmakefile.deps:
 	$(CXX) $(strip $(CXXFLAGS)) -MM *.cpp > GNUmakefile.deps
 
 # CXXFLAGS are tuned earlier.
-.PHONY: asan ubsan no-asm
-no-asm asan ubsan: libcryptopp.a cryptest.exe
+.PHONY: native no-asm asan ubsan
+native no-asm asan ubsan: libcryptopp.a cryptest.exe
 
 # CXXFLAGS are tuned earlier. Applications must use linker flags
 #  -Wl,--gc-sections (Linux and Unix) or -Wl,-dead_strip (OS X)