diff -Naur grass-7.8.3.org/include/Make/HtmlRules.make grass-7.8.3/include/Make/HtmlRules.make
--- grass-7.8.3.org/include/Make/HtmlRules.make	2020-05-05 10:51:50.000000000 +0200
+++ grass-7.8.3/include/Make/HtmlRules.make	2020-10-10 13:43:42.800880621 +0200
@@ -11,10 +11,10 @@
 endif
 
 $(HTMLDIR)/%.png: %.png | $(HTMLDIR)
-	$(INSTALL_DATA) $< $@
+	flock $@ $(INSTALL_DATA) $< $@
 
 $(HTMLDIR)/%.jpg: %.jpg | $(HTMLDIR)
-	$(INSTALL_DATA) $< $@
+	flock $@ $(INSTALL_DATA) $< $@
 
 $(HTMLDIR)/%.gif: %.gif | $(HTMLDIR)
-	$(INSTALL_DATA) $< $@
+	flock $@ $(INSTALL_DATA) $< $@