Fix intermittent build failure

1 files changed, 4 insertions, 2 deletions

diff --git a/Makefile b/Makefile
index 3c8e8f8..8dc01e7 100644
--- a/Makefile
+++ b/Makefile
@@ -41,10 +41,12 @@ $(OUTDIR)/quatuor.html: quatuor.md
 $(OUTDIR)/programmes.html: programs.in
 
 # Rules for automatic, incremental folder creation.
-# ⚠ Fail for intermediate folders which hold only subdirs.
 
+# Our lists of target directories are created from the lists of leaf
+# resources; some intermediate directories that only hold subdirs do
+# not appear in these lists.  Work around that with -p.
 $(OUTDIR) $(images_folders) $(stylesheets_folders):
-	mkdir $@
+	mkdir -p $@
 
 .SECONDEXPANSION:
 $(resources) $(images) $(stylesheets) $(pages) $(members_pages): | $$(@D)