diff --git a/External/AvalonTools/CMakeLists.txt b/External/AvalonTools/CMakeLists.txt
index 1c04dcdd8..86c968236 100755
--- a/External/AvalonTools/CMakeLists.txt
+++ b/External/AvalonTools/CMakeLists.txt
@@ -19,7 +19,9 @@ if(needDownload)
   if(NOT DEFINED AVALONTOOLS_MD5SUM)
     set(AVALONTOOLS_MD5SUM "092a94f421873f038aa67d4a6cc8cb54")
   endif()
-  string(REGEX REPLACE "^.*/" "" AVALONTOOLS_BASE "${AVALONTOOLS_URL}")
+  if(NOT DEFINED AVALONTOOLS_BASE)
+    string(REGEX REPLACE "^.*/" "" AVALONTOOLS_BASE "${AVALONTOOLS_URL}")
+  endif()
   downloadAndCheckMD5(${AVALONTOOLS_URL} "${CMAKE_CURRENT_SOURCE_DIR}/${AVALONTOOLS_BASE}" ${AVALONTOOLS_MD5SUM})
   execute_process(COMMAND ${CMAKE_COMMAND} -E tar xf
     ${CMAKE_CURRENT_SOURCE_DIR}/AvalonToolkit_1.2.0.source.tar
diff --git a/External/INCHI-API/CMakeLists.txt b/External/INCHI-API/CMakeLists.txt
index fe17c86c6..2e0c454e1 100644
--- a/External/INCHI-API/CMakeLists.txt
+++ b/External/INCHI-API/CMakeLists.txt
@@ -21,7 +21,9 @@ if(RDK_BUILD_INCHI_SUPPORT)
       if(NOT DEFINED INCHI_MD5SUM)
         set(INCHI_MD5SUM "8447bf108af12fe66eecba41bbc89918")
       endif()
-      string(REGEX REPLACE "^.*/" "" INCHI_BASE "${INCHI_URL}")
+      if(NOT DEFINED INCHI_BASE)
+        string(REGEX REPLACE "^.*/" "" INCHI_BASE "${INCHI_URL}")
+      endif()
       downloadAndCheckMD5(${INCHI_URL} "${CMAKE_CURRENT_SOURCE_DIR}/${INCHI_BASE}" ${INCHI_MD5SUM})
       execute_process(COMMAND ${CMAKE_COMMAND} -E tar xf
         ${CMAKE_CURRENT_SOURCE_DIR}/INCHI-1-API.zip