diff --git a/GNUmakefile b/GNUmakefile
index 68972f99..2ea6bf91 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -353,7 +353,7 @@ TEST_DB    ?= $(shell [ -d /dev/shm ] && echo /dev/shm || echo /tmp)/mdbx-test.d
 TEST_LOG   ?= $(shell [ -d /dev/shm ] && echo /dev/shm || echo /tmp)/mdbx-test.log
 TEST_OSAL  := $(shell $(uname2osal))
 TEST_ITER  := $(shell $(uname2titer))
-TEST_SRC   := test/osal-$(TEST_OSAL).c++ $(filter-out $(wildcard test/osal-*.c++), $(wildcard test/*.c++))
+TEST_SRC   := test/osal-$(TEST_OSAL).c++ $(filter-out $(wildcard test/osal-*.c++),$(wildcard test/*.c++)) $(call select_by,MDBX_BUILD_CXX,,src/mdbx.c++)
 TEST_INC   := $(wildcard test/*.h++)
 TEST_OBJ   := $(patsubst %.c++,%.o,$(TEST_SRC))
 TAR        ?= $(shell which gnu-tar || echo tar)