Index: cmake/FindLibSpectre.cmake
--- cmake/FindLibSpectre.cmake.orig
+++ cmake/FindLibSpectre.cmake
@@ -39,12 +39,16 @@ if(_pc_LIBSPECTRE_FOUND)
     HINTS ${_pc_LIBSPECTRE_LIBRARY_DIRS} ${CMAKE_LIBRARY_PATH}
   )
 
-  find_path(LIBSPECTRE_INCLUDE_DIR spectre.h
-    HINTS ${_pc_LIBSPECTRE_INCLUDE_DIRS}
-    PATH_SUFFIXES libspectre
-  )
+  if (_pc_LIBSPECTRE_INCLUDE_DIRS)
+    set(LIBSPECTRE_INCLUDE_DIR ${_pc_LIBSPECTRE_INCLUDE_DIRS})
+  else()
+    find_path(LIBSPECTRE_INCLUDE_DIR spectre.h
+      HINTS ${_pc_LIBSPECTRE_INCLUDE_DIRS}
+      PATH_SUFFIXES libspectre
+    )
+  endif()
 
-  set(LIBSPECTRE_FOUND TRUE)
+  set(LIBSPECTRE_INTERNAL_FOUND TRUE)
 endif(_pc_LIBSPECTRE_FOUND)
 
 include(FindPackageHandleStandardArgs)