diff --git a/build.vars b/build.vars
index a76f00c..4d93da1 100644
--- a/build.vars
+++ b/build.vars
@@ -53,7 +53,7 @@ export PATH="${PREFIX}/bin${PATH:+:${PATH}}";
 : ${LOG_MSG_WARN_COLOUR:=96};
 : ${TARBALL_FNAME_PREFIX:=midipix-${ARCH}-${BUILD}.};
 : ${TARBALL_SIGN_GPG_KEY:=};
-: ${TARBALL_SRC_FNAME_PREFIX:=midipix-${ARCH}-${BUILD}.src.};
+: ${TARBALL_SRC_FNAME_PREFIX:=midipix-${ARCH}-${BUILD}_src.};
 : ${TARBALL_SRC_SIGN_GPG_KEY:=};
 : ${TARBALL_SUFFIX:=xz};
 : ${TIMESTAMP_FMT_STATUS_FILES:=%Y-%m-%d-%H-%M-%S};