--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -374,6 +374,9 @@
   find_package( Backtrace )
   if ( Backtrace_FOUND )
     set ( HAVE_BACKTRACE 1 )
+  else ()
+    set ( Backtrace_LIBRARY "" )
+    set ( Backtrace_HEADER "" )
   endif ()
 endif ()
 check_cxx_source_compiles( "#include <cxxabi.h>
