diff --git a/Makefile b/Makefile
index b5a6d602b2..90e05ac409 100644
--- a/Makefile
+++ b/Makefile
@@ -256,8 +256,7 @@ GENERATED_FILES += $(KEYCODEMAP_FILES)
 
 ui/input-keymap-%.c: $(KEYCODEMAP_GEN) $(KEYCODEMAP_CSV) $(SRC_PATH)/ui/Makefile.objs
 	$(call quiet-command,\
-	    src=$$(echo $@ | sed -E -e "s,^ui/input-keymap-(.+)-to-(.+)\.c$$,\1,") && \
-	    dst=$$(echo $@ | sed -E -e "s,^ui/input-keymap-(.+)-to-(.+)\.c$$,\2,") && \
+	    stem=$* && src=$${stem%-to-*} dst=$${stem#*-to-} && \
 	    test -e $(KEYCODEMAP_GEN) && \
 	    $(PYTHON) $(KEYCODEMAP_GEN) \
 	          --lang glib2 \