diff --git a/build.subr b/build.subr
index d4b00e1..2308a9f 100644
--- a/build.subr
+++ b/build.subr
@@ -306,8 +306,12 @@ update_build_status() {
 	while [ ${#} -gt 0 ]; do
 	case ${1} in
 	build_start)
-		touch ${BUILD_STATUS_IN_PROGRESS_FNAME};
-		touch ${BUILD_STATUS_PROGRESS_FNAME:=${PREFIX}/BUILD_STARTED_AT_${BUILD_DATE_START:=$(date %Y-%m-%d-%H-%M-%S)}};
+		if [ -f ${BUILD_STATUS_IN_PROGRESS_FNAME} ]; then
+			log_msg failexit "Error: build already in progress.";
+		else
+			touch ${BUILD_STATUS_IN_PROGRESS_FNAME};
+			touch ${BUILD_STATUS_PROGRESS_FNAME:=${PREFIX}/BUILD_STARTED_AT_${BUILD_DATE_START:=$(date %Y-%m-%d-%H-%M-%S)}};
+		fi;
 		;;
 	build_finish)
 		if [ -f ${BUILD_STATUS_PROGRESS_FNAME} ]; then