Index: lldb/trunk/cmake/modules/LLDBStandalone.cmake
===================================================================
--- lldb/trunk/cmake/modules/LLDBStandalone.cmake
+++ lldb/trunk/cmake/modules/LLDBStandalone.cmake
@@ -23,6 +23,7 @@
     else()
       get_filename_component(LLVM_MAIN_SRC_DIR ${LLDB_PATH_TO_LLVM_SOURCE}
                              ABSOLUTE)
+      set(LLVM_MAIN_INCLUDE_DIR "${LLVM_MAIN_SRC_DIR}/include")
       list(APPEND CMAKE_MODULE_PATH "${LLVM_MAIN_SRC_DIR}/cmake/modules")
     endif()
   endif()
@@ -30,15 +31,27 @@
   if (LLDB_PATH_TO_CLANG_SOURCE)
       get_filename_component(CLANG_MAIN_SRC_DIR ${LLDB_PATH_TO_CLANG_SOURCE}
                              ABSOLUTE)
+      set(CLANG_MAIN_INCLUDE_DIR "${CLANG_MAIN_SRC_DIR}/include")
   endif()
 
   list(APPEND CMAKE_MODULE_PATH "${LLDB_PATH_TO_LLVM_BUILD}/share/llvm/cmake")
 
-  get_filename_component(PATH_TO_LLVM_BUILD ${LLDB_PATH_TO_LLVM_BUILD}
-                         ABSOLUTE)
+  if (LLDB_PATH_TO_LLVM_BUILD)
+    get_filename_component(PATH_TO_LLVM_BUILD ${LLDB_PATH_TO_LLVM_BUILD}
+                           ABSOLUTE)
+  else()
+    message(FATAL_ERROR "Please set LLDB_PATH_TO_LLVM_BUILD to the root "
+            "directory of LLVM build or install site.")
+  endif()
+
+  if (LLDB_PATH_TO_CLANG_BUILD)
+    get_filename_component(PATH_TO_CLANG_BUILD ${LLDB_PATH_TO_CLANG_BUILD}
+                           ABSOLUTE)
+  else()
+    message(FATAL_ERROR "Please set LLDB_PATH_TO_CLANG_BUILD to the root "
+            "directory of Clang build or install site.")
+  endif()
 
-  get_filename_component(PATH_TO_CLANG_BUILD ${LLDB_PATH_TO_CLANG_BUILD}
-                         ABSOLUTE)
 
   # These variables are used by add_llvm_library.
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
@@ -67,11 +80,8 @@
 
   set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
 
-  set(LLVM_MAIN_INCLUDE_DIR "${LLVM_MAIN_SRC_DIR}/include")
   set(LLVM_BINARY_DIR ${CMAKE_BINARY_DIR})
 
-  set(CLANG_MAIN_INCLUDE_DIR "${CLANG_MAIN_SRC_DIR}/include")
-
   set(CMAKE_INCLUDE_CURRENT_DIR ON)
   include_directories("${PATH_TO_LLVM_BUILD}/include"
                       "${LLVM_MAIN_INCLUDE_DIR}"