diff --git a/testing/Makefile b/testing/Makefile
index 122262f865..e83ec09396 100644
--- a/testing/Makefile
+++ b/testing/Makefile
@@ -17,8 +17,8 @@ make-brief:
 
 coverage:
 	@for repo in $(DIRS); do (cd $$repo && echo "Coverage for '$$repo' dir:" && make -s coverage); done
-	@test -f btest/coverage.log && cp btest/coverage.log `mktemp brocov.tmp.XXX` || true
-	@for f in external/*/coverage.log; do test -f $$f && cp $$f `mktemp brocov.tmp.XXX` || true; done
+	@test -f btest/coverage.log && cp btest/coverage.log `mktemp brocov.tmp.XXXXXX` || true
+	@for f in external/*/coverage.log; do test -f $$f && cp $$f `mktemp brocov.tmp.XXXXXX` || true; done
 	@echo "Complete test suite code coverage:"
 	@./scripts/coverage-calc "brocov.tmp.*" coverage.log `pwd`/../scripts
 	@rm -f brocov.tmp.*