diff --git a/make/defs.mk b/make/defs.mk
index 3b551968..1fd78b8a 100644
--- a/make/defs.mk
+++ b/make/defs.mk
@@ -368,7 +368,7 @@ BUILD_HDRDIR_BASE     ?= $(TOPDIR)/include
 BUILD_HDRDIR          ?= $(BUILD_HDRDIR_BASE)/$(HDRDIR_SCOPE_SUFFIX)
 SRC_H                 += $(filter %.h %.H %.hpp, $(SRC_ALL_CPP))
 BUILD_H                = $(addprefix $(BUILD_HDRDIR)/,$(SRC_H))
-BUILD_HDR              = $(addprefix $(BUILD_HDRDIR)/,$(SRC_H))
+BUILD_HDR             += $(addprefix $(BUILD_HDRDIR)/,$(SRC_H))
 INSTALL_HDRDIR        ?= $(PREFIX)/include
 INSTALLED_HDR         += $(addprefix $(INSTALL_HDRDIR)/,$(SRC_H))
 
@@ -1073,7 +1073,7 @@ all:
 nothing:
 
 echo-vars:
-	make -p nothing | grep -B1 "^[A-Z_]* *[?:]*="
+	make -p nothing | grep -B1 "^[A-Z_]* *[?:+]*="
 
 echo-makefiles:
 	strace -f make nothing 2>&1 | sed '/open\(at\)*(.*\(Makefile\|\.mk\)/ !d; s/.*open("//; s/.*openat([A-Z_]\+, "//; s/", O_.*//'