diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -104,6 +104,11 @@
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
+if (NOT LLVM_DEFAULT_TARGET_TRIPLE)
+  include(GetHostTriple)
+  get_host_triple(LLVM_DEFAULT_TARGET_TRIPLE)
+endif()
+
 # Use libtool instead of ar if you are both on an Apple host, and targeting Apple.
 if(CMAKE_HOST_APPLE AND APPLE)
   include(UseLibtool)