diff --git a/src/library/tools/Makefile.in b/src/library/tools/Makefile.in
index 8a0b070013..08bbda3410 100644
--- a/src/library/tools/Makefile.in
+++ b/src/library/tools/Makefile.in
@@ -47,8 +47,9 @@ all: Makefile DESCRIPTION
 
 mkR: mkR1
 
+## avoid "$<" as that was empty when using bmake (tested 20200710 and 20241124)
 $(WRE_DATA): $(WRE_SRC)
-	@grep -E '^@(api|eapi|emb)(fun|var|hdr)' $< > $@
+	@grep -E '^@(api|eapi|emb)(fun|var|hdr)' "$(WRE_SRC)" > "$@"
 
 include $(top_srcdir)/share/make/basepkg.mk