diff --git a/sources/CMakeLists.txt b/sources/CMakeLists.txt
index 9ef77aa4..b6f0c57c 100644
--- a/sources/CMakeLists.txt
+++ b/sources/CMakeLists.txt
@@ -32,7 +32,7 @@ set(CC_EXTERNAL_SOURCES
   ${CMAKE_CURRENT_LIST_DIR}/tommyds/tommy.h
 )
 
-if(USE_MODULES)
+if(NOT USE_MODULES)
   list(APPEND CC_EXTERNAL_SOURCES 
     ${CC_UNZIP_SOURCES}
     ${CC_TINYDIR_SOURCES}