diff --git a/build_tools/download_externals b/build_tools/download_externals
index 62b128aaa7ac44894135d9f213d6a94378043ac6..f27271fd5a53cf9f434f4ff565d33c76236c4288 100755
--- a/build_tools/download_externals
+++ b/build_tools/download_externals
@@ -165,7 +165,7 @@ if [[ -f ${DESTDIR}${ASTMODDIR}/${module_name}.manifest.xml ]] ; then
 					fi
 				fi
 
-				cs=$(md5sum ${f} | cut -b1-32)
+				cs=$(${MD5} ${f} | cut -b1-32)
 				if [[ "${cs}" !=  "${sum}" ]] ; then
 					echo Checksum mismatch: ${f}
 					need_install=1