diff --git a/rules.mk b/rules.mk
index 7a40d1de..83c9da5f 100644
--- a/rules.mk
+++ b/rules.mk
@@ -565,6 +565,7 @@ $(OBJDIR)/%.o : %.cpp
 # Assemble: create object files from assembler source files.
 $(OBJDIR)/%.o : %.S
 	@echo
+	mkdir -p $(@D)
 	@echo $(MSG_ASSEMBLING) $<
 	$(CC) -c $(ALL_ASFLAGS) $< -o $@