diff --git a/Modules/UseSWIG.cmake b/Modules/UseSWIG.cmake
index 6d3f1debf..be15b52f1 100644
--- a/Modules/UseSWIG.cmake
+++ b/Modules/UseSWIG.cmake
@@ -124,6 +124,7 @@ ENDMACRO(SWIG_MODULE_INITIALIZE)
 #
 
 MACRO(SWIG_GET_EXTRA_OUTPUT_FILES language outfiles generatedpath infile)
+  SET(${outfiles} "")
   GET_SOURCE_FILE_PROPERTY(SWIG_GET_EXTRA_OUTPUT_FILES_module_basename
     ${infile} SWIG_MODULE_NAME)
   IF(SWIG_GET_EXTRA_OUTPUT_FILES_module_basename STREQUAL "NOTFOUND")