diff --git a/lib/Target/CBackend/CBackend.cpp b/lib/Target/CBackend/CBackend.cpp
index 4e86c6f..9041012 100644
--- a/lib/Target/CBackend/CBackend.cpp
+++ b/lib/Target/CBackend/CBackend.cpp
@@ -813,7 +813,7 @@
       << "extern void *__builtin_alloca(unsigned int);\n"
       << "#endif\n"
       << "#define alloca(x) __builtin_alloca(x)\n"
-      << "#elif defined(__FreeBSD__)\n"
+      << "#elif defined(__FreeBSD__) || defined(__OpenBSD__)\n"
       << "#define alloca(x) __builtin_alloca(x)\n"
       << "#elif !defined(_MSC_VER)\n"
       << "#include <alloca.h>\n"
diff --git a/lib/Target/CBackend/Writer.cpp b/lib/Target/CBackend/Writer.cpp
index 4e86c6f..9041012 100644
--- a/lib/Target/CBackend/Writer.cpp
+++ b/lib/Target/CBackend/Writer.cpp
@@ -813,7 +813,7 @@
       << "extern void *__builtin_alloca(unsigned int);\n"
       << "#endif\n"
       << "#define alloca(x) __builtin_alloca(x)\n"
-      << "#elif defined(__FreeBSD__)\n"
+      << "#elif defined(__FreeBSD__) || defined(__OpenBSD__)\n"
       << "#define alloca(x) __builtin_alloca(x)\n"
       << "#elif !defined(_MSC_VER)\n"
       << "#include <alloca.h>\n"