Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -533,7 +533,7 @@
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND UBSAN_SUPPORTED_ARCH AND
-    OS_NAME MATCHES "Darwin|Linux|FreeBSD|Windows|Android|Fuchsia")
+    OS_NAME MATCHES "Darwin|Linux|FreeBSD|NetBSD|Windows|Android|Fuchsia")
   set(COMPILER_RT_HAS_UBSAN TRUE)
 else()
   set(COMPILER_RT_HAS_UBSAN FALSE)
Index: lib/ubsan/ubsan_platform.h
===================================================================
--- lib/ubsan/ubsan_platform.h
+++ lib/ubsan/ubsan_platform.h
@@ -14,9 +14,10 @@
 #define UBSAN_PLATFORM_H
 
 // Other platforms should be easy to add, and probably work as-is.
-#if (defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__)) && \
-    (defined(__x86_64__) || defined(__i386__) || defined(__arm__) || \
-     defined(__aarch64__) || defined(__mips__) || defined(__powerpc64__) || \
+#if (defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__) ||       \
+     defined(__NetBSD__)) &&                                                   \
+    (defined(__x86_64__) || defined(__i386__) || defined(__arm__) ||           \
+     defined(__aarch64__) || defined(__mips__) || defined(__powerpc64__) ||    \
      defined(__s390__))
 # define CAN_SANITIZE_UB 1
 #elif defined(_WIN32) || defined(__Fuchsia__)
Index: test/ubsan/TestCases/Float/cast-overflow.cpp
===================================================================
--- test/ubsan/TestCases/Float/cast-overflow.cpp
+++ test/ubsan/TestCases/Float/cast-overflow.cpp
@@ -18,11 +18,17 @@
 # define BYTE_ORDER __DARWIN_BYTE_ORDER
 # define BIG_ENDIAN __DARWIN_BIG_ENDIAN
 # define LITTLE_ENDIAN __DARWIN_LITTLE_ENDIAN
-#elif defined(__FreeBSD__)
+#elif defined(__FreeBSD__) || defined(__NetBSD__)
 # include <sys/endian.h>
-# define BYTE_ORDER _BYTE_ORDER
-# define BIG_ENDIAN _BIG_ENDIAN
-# define LITTLE_ENDIAN _LITTLE_ENDIAN
+# ifndef BYTE_ORDER
+#  define BYTE_ORDER _BYTE_ORDER
+# endif
+# ifndef BIG_ENDIAN
+#  define BIG_ENDIAN _BIG_ENDIAN
+# endif
+# ifndef LITTLE_ENDIAN
+#  define LITTLE_ENDIAN _LITTLE_ENDIAN
+# endif
 #elif defined(_WIN32)
 # define BYTE_ORDER 0
 # define BIG_ENDIAN 1
Index: test/ubsan/lit.common.cfg
===================================================================
--- test/ubsan/lit.common.cfg
+++ test/ubsan/lit.common.cfg
@@ -70,7 +70,7 @@
 config.suffixes = ['.c', '.cc', '.cpp']
 
 # Check that the host supports UndefinedBehaviorSanitizer tests
-if config.host_os not in ['Linux', 'Darwin', 'FreeBSD', 'Windows']:
+if config.host_os not in ['Linux', 'Darwin', 'FreeBSD', 'Windows', 'NetBSD']:
   config.unsupported = True
 
 # Allow tests to use REQUIRES=stable-runtime.  For use when you cannot use XFAIL