diff --git a/openmp/CMakeLists.txt b/openmp/CMakeLists.txt
--- a/openmp/CMakeLists.txt
+++ b/openmp/CMakeLists.txt
@@ -66,6 +66,20 @@
   set(ENABLE_LIBOMPTARGET OFF)
 endif()
 
+# Attempt to locate LLVM source, required by libomptarget
+if (NOT LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR)
+  if (LLVM_MAIN_INCLUDE_DIR)
+    set(LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR ${LLVM_MAIN_INCLUDE_DIR})
+  elseif (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/../llvm/include)
+    set(LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../llvm/include)
+  endif()
+endif()
+
+if (NOT LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR)
+  message(STATUS "Missing definition for LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR, disabling libomptarget")
+  set(ENABLE_LIBOMPTARGET OFF)
+endif()
+
 option(OPENMP_ENABLE_LIBOMPTARGET "Enable building libomptarget for offloading."
        ${ENABLE_LIBOMPTARGET})
 if (OPENMP_ENABLE_LIBOMPTARGET)
diff --git a/openmp/libomptarget/CMakeLists.txt b/openmp/libomptarget/CMakeLists.txt
--- a/openmp/libomptarget/CMakeLists.txt
+++ b/openmp/libomptarget/CMakeLists.txt
@@ -29,6 +29,11 @@
 # Get dependencies for the different components of the project.
 include(LibomptargetGetDependencies)
 
+# LLVM source tree is required at build time for libomptarget
+if (NOT LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR)
+  message(FATAL_ERROR "Missing definition for LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR")
+endif()
+
 # This is a list of all the targets that are supported/tested right now.
 set (LIBOMPTARGET_ALL_TARGETS "${LIBOMPTARGET_ALL_TARGETS} aarch64-unknown-linux-gnu")
 set (LIBOMPTARGET_ALL_TARGETS "${LIBOMPTARGET_ALL_TARGETS} powerpc64le-ibm-linux-gnu")
diff --git a/openmp/libomptarget/plugins/amdgpu/CMakeLists.txt b/openmp/libomptarget/plugins/amdgpu/CMakeLists.txt
--- a/openmp/libomptarget/plugins/amdgpu/CMakeLists.txt
+++ b/openmp/libomptarget/plugins/amdgpu/CMakeLists.txt
@@ -30,8 +30,8 @@
   return()
 endif()
 
-if (NOT LLVM_MAIN_INCLUDE_DIR)
-  libomptarget_say("Not building AMDGPU plugin: Missing definition for LLVM_MAIN_INCLUDE_DIR")
+if (NOT LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR)
+  libomptarget_say("Not building AMDGPU plugin: Missing definition for LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR")
   return()
 endif()
 
@@ -50,7 +50,7 @@
 
 include_directories(
   ${CMAKE_CURRENT_SOURCE_DIR}/impl
-  ${LLVM_MAIN_INCLUDE_DIR}
+  ${LIBOMPTARGET_LLVM_MAIN_INCLUDE_DIR}
 )
 
 add_library(omptarget.rtl.amdgpu SHARED