diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index 62ecd1e28ce6..7843fde5c456 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -4679,8 +4679,10 @@ class ARMTargetInfo : public TargetInfo {
     DoubleAlign = LongLongAlign = LongDoubleAlign = SuitableAlign = 64;
     const llvm::Triple &T = getTriple();
 
-    // size_t is unsigned long on MachO-derived environments, NetBSD and Bitrig.
+    // size_t is unsigned long on MachO-derived environments, NetBSD,
+    // OpenBSD and Bitrig.
     if (T.isOSBinFormatMachO() || T.getOS() == llvm::Triple::NetBSD ||
+        T.getOS() == llvm::Triple::OpenBSD ||
         T.getOS() == llvm::Triple::Bitrig)
       SizeType = UnsignedLong;
     else
@@ -4688,6 +4690,7 @@ class ARMTargetInfo : public TargetInfo {
 
     switch (T.getOS()) {
     case llvm::Triple::NetBSD:
+    case llvm::Triple::OpenBSD:
       WCharType = SignedInt;
       break;
     case llvm::Triple::Win32:
@@ -4885,6 +4888,7 @@ public:
 
     switch (getTriple().getOS()) {
     case llvm::Triple::NetBSD:
+    case llvm::Triple::OpenBSD:
       PtrDiffType = SignedLong;
       break;
     default:
diff --git a/clang/test/Preprocessor/init.c b/clang/test/Preprocessor/init.c
index 5a0b268d8472..16342332b847 100644
--- a/clang/test/Preprocessor/init.c
+++ b/clang/test/Preprocessor/init.c
@@ -8463,6 +8463,29 @@
 // RUN: %clang_cc1 -triple lanai-unknown-unknown -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix LANAI %s
 // LANAI: #define __lanai__ 1
 //
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=amd64-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=arm-unknown-openbsd6.1-gnueabi < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=i386-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=sparc64-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
+// OPENBSD:#define __ELF__ 1
+// OPENBSD:#define __INT16_TYPE__ short
+// OPENBSD:#define __INT32_TYPE__ int
+// OPENBSD:#define __INT64_TYPE__ long long int
+// OPENBSD:#define __INT8_TYPE__ signed char
+// OPENBSD:#define __INTMAX_TYPE__ long long int
+// OPENBSD:#define __INTPTR_TYPE__ long int
+// OPENBSD:#define __OpenBSD__ 1
+// OPENBSD:#define __PTRDIFF_TYPE__ long int
+// OPENBSD:#define __SIZE_TYPE__ long unsigned int
+// OPENBSD:#define __UINT16_TYPE__ unsigned short
+// OPENBSD:#define __UINT32_TYPE__ unsigned int
+// OPENBSD:#define __UINT64_TYPE__ long long unsigned int
+// OPENBSD:#define __UINT8_TYPE__ unsigned char
+// OPENBSD:#define __UINTMAX_TYPE__ long long unsigned int
+// OPENBSD:#define __UINTPTR_TYPE__ long unsigned int
+// OPENBSD:#define __WCHAR_TYPE__ int
+// OPENBSD:#define __WINT_TYPE__ int
+//
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc64-unknown-freebsd < /dev/null | FileCheck -match-full-lines -check-prefix PPC64-FREEBSD %s
 // PPC64-FREEBSD-NOT: #define __LONG_DOUBLE_128__ 1
 //