diff --git a/GNUmakefile b/GNUmakefile
index 873ce226..c826c5e5 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -6,6 +6,22 @@
 #
 ################################################################################
 #
+# Basic internal definitios. For a customizable variables and options see below.
+#
+$(info // The GNU Make $(MAKE_VERSION))
+SHELL         := $(shell env bash -c 'echo $$BASH')
+MAKE_VERx3    := $(shell printf "%3s%3s%3s" $(subst ., ,$(MAKE_VERSION)))
+make_lt_3_81  := $(shell expr "$(MAKE_VERx3)" "<" "  3 81")
+ifeq ($(make_lt_3_81),1)
+$(error Please use GNU Make 3.81 or above)
+endif
+make_lt_4_1   := $(shell expr "$(MAKE_VERx3)" "<" "  4  1")
+SRC_PROBE_C   := $(shell [ -f mdbx.c ] && echo mdbx.c || echo src/osal.c)
+SRC_PROBE_CXX := $(shell [ -f mdbx.c++ ] && echo mdbx.c++ || echo src/mdbx.c++)
+UNAME         := $(shell uname -s 2>/dev/null || echo Unknown)
+#
+################################################################################
+#
 # Use `make options` to list the available libmdbx build options.
 #
 # Note that the defaults should already be correct for most platforms;
@@ -13,39 +29,48 @@
 # in README and source code (see src/options.h) if you do.
 #
 
-SHELL   := env bash
-
 # install sandbox
 DESTDIR ?=
-
+INSTALL ?= install
 # install prefixes (inside sandbox)
 prefix  ?= /usr/local
 mandir  ?= $(prefix)/man
-
 # lib/bin suffix for multiarch/biarch, e.g. '.x86_64'
 suffix  ?=
 
-INSTALL ?= install
+# toolchain
 CC      ?= gcc
 CXX     ?= g++
 CFLAGS_EXTRA ?=
 LD      ?= ld
+
+# build options
 MDBX_BUILD_OPTIONS ?=-DNDEBUG=1
 MDBX_BUILD_TIMESTAMP ?=$(shell date +%Y-%m-%dT%H:%M:%S%z)
-CFLAGS  ?= $(strip $(eval CFLAGS := -std=gnu11 -O2 -g -Wall -Werror -Wextra -Wpedantic -ffunction-sections -fPIC -fvisibility=hidden -pthread -Wno-error=attributes $$(shell PROBE=$$$$([ -f mdbx.c ] && echo mdbx.c || echo src/osal.c); for opt in -fno-semantic-interposition -Wno-unused-command-line-argument -Wno-tautological-compare; do [ -z "$$$$($(CC) '-DMDBX_BUILD_FLAGS="probe"' $$$${opt} -c $$$${PROBE} -o /dev/null >/dev/null 2>&1 || echo failed)" ] && echo "$$$${opt} "; done)$(CFLAGS_EXTRA))$(CFLAGS))
-# Choosing C++ standard with deferred simple variable expansion trick
-CXXSTD  ?= $(eval CXXSTD := $$(shell PROBE=$$$$([ -f mdbx.c++ ] && echo mdbx.c++ || echo src/mdbx.c++); for std in gnu++23 c++23 gnu++2b c++2b gnu++20 c++20 gnu++2a c++2a gnu++17 c++17 gnu++1z c++1z gnu++14 c++14 gnu++1y c++1y gnu+11 c++11 gnu++0x c++0x; do $(CXX) -std=$$$${std} -c $$$${PROBE} -o /dev/null 2>probe4std-$$$${std}.err >/dev/null && echo "-std=$$$${std}" && exit; done))$(CXXSTD)
-CXXFLAGS = $(strip $(CXXSTD) $(filter-out -std=gnu11,$(CFLAGS)))
 
-# TIP: Try append '--no-as-needed,-lrt' for ability to built with modern glibc, but then use with the old.
-LIBS    ?= $(shell $(uname2libs))
-LDFLAGS ?= $(shell $(uname2ldflags))
-EXE_LDFLAGS ?= -pthread
-LIB_STDCXXFS ?= $(eval LIB_STDCXXFS := $$(shell echo 'int main(void) { MDBX_STD_FILESYSTEM_PATH probe; return probe.is_absolute(); }' | cat mdbx.h++ - | sed $$$$'1s/\xef\xbb\xbf//' | $(CXX) -x c++ $(CXXFLAGS) - -Wl,--allow-multiple-definition -lstdc++fs $(LIBS) $(LDFLAGS) $(EXE_LDFLAGS) -o /dev/null 2>probe4lstdfs.err >/dev/null && echo '-Wl,--allow-multiple-definition -lstdc++fs'))$(LIB_STDCXXFS)
+# probe and compose common compiler flags with variable expansion trick (seems this work two times per session for GNU Make 3.81)
+CFLAGS       ?= $(strip $(eval CFLAGS := -std=gnu11 -O2 -g -Wall -Werror -Wextra -Wpedantic -ffunction-sections -fPIC -fvisibility=hidden -pthread -Wno-error=attributes $$(shell for opt in -fno-semantic-interposition -Wno-unused-command-line-argument -Wno-tautological-compare; do [ -z "$$$$($(CC) '-DMDBX_BUILD_FLAGS="probe"' $$$${opt} -c $(SRC_PROBE_C) -o /dev/null >/dev/null 2>&1 || echo failed)" ] && echo "$$$${opt} "; done)$(CFLAGS_EXTRA))$(CFLAGS))
+
+# choosing C++ standard with variable expansion trick (seems this work two times per session for GNU Make 3.81)
+CXXSTD       ?= $(eval CXXSTD := $$(shell for std in gnu++23 c++23 gnu++2b c++2b gnu++20 c++20 gnu++2a c++2a gnu++17 c++17 gnu++1z c++1z gnu++14 c++14 gnu++1y c++1y gnu+11 c++11 gnu++0x c++0x; do $(CXX) -std=$$$${std} -c $(SRC_PROBE_CXX) -o /dev/null 2>probe4std-$$$${std}.err >/dev/null && echo "-std=$$$${std}" && exit; done))$(CXXSTD)
+CXXFLAGS     ?= $(strip $(CXXSTD) $(filter-out -std=gnu11,$(CFLAGS)))
+
+# libraries adn options for linking
+EXE_LDFLAGS  ?= -pthread
+ifeq ($(make_lt_4_1),1)
+# don't use variable expansion trick as workaround for bugs of GNU Make before 4.1
+LIBS         ?= $(shell $(uname2libs))
+LDFLAGS      ?= $(shell $(uname2ldflags))
+LIB_STDCXXFS ?= $(shell echo 'int main(void) { MDBX_STD_FILESYSTEM_PATH probe; return probe.is_absolute(); }' | cat mdbx.h++ - | sed $$'1s/\xef\xbb\xbf//' | $(CXX) -x c++ $(CXXFLAGS) -Wno-error - -Wl,--allow-multiple-definition -lstdc++fs $(LIBS) $(LDFLAGS) $(EXE_LDFLAGS) -o /dev/null 2>probe4lstdfs.err >/dev/null && echo '-Wl,--allow-multiple-definition -lstdc++fs')
+else
+# using variable expansion trick to avoid repeaded probes
+LIBS         ?= $(eval LIBS := $$(shell $$(uname2libs)))$(LIBS)
+LDFLAGS      ?= $(eval LDFLAGS := $$(shell $$(uname2ldflags)))$(LDFLAGS)
+LIB_STDCXXFS ?= $(eval LIB_STDCXXFS := $$(shell echo 'int main(void) { MDBX_STD_FILESYSTEM_PATH probe; return probe.is_absolute(); }' | cat mdbx.h++ - | sed $$$$'1s/\xef\xbb\xbf//' | $(CXX) -x c++ $(CXXFLAGS) -Wno-error - -Wl,--allow-multiple-definition -lstdc++fs $(LIBS) $(LDFLAGS) $(EXE_LDFLAGS) -o /dev/null 2>probe4lstdfs.err >/dev/null && echo '-Wl,--allow-multiple-definition -lstdc++fs'))$(LIB_STDCXXFS)
+endif
 
 ################################################################################
 
-UNAME      := $(shell uname -s 2>/dev/null || echo Unknown)
 define uname2sosuffix
   case "$(UNAME)" in
     Darwin*|Mach*) echo dylib;;
@@ -53,33 +78,37 @@ define uname2sosuffix
     *) echo so;;
   esac
 endef
+
 define uname2ldflags
   case "$(UNAME)" in
     CYGWIN*|MINGW*|MSYS*|Windows*)
-      echo '-Wl,--gc-sections,-O1'
+      echo '-Wl,--gc-sections,-O1';
       ;;
     *)
-      "$(LD)" --help 2>/dev/null | grep -q -- --gc-sections && echo '-Wl,--gc-sections,-z,relro,-O1'
-      "$(LD)" --help 2>/dev/null | grep -q -- -dead_strip && echo '-Wl,-dead_strip'
+      $(LD) --help 2>/dev/null | grep -q -- --gc-sections && echo '-Wl,--gc-sections,-z,relro,-O1';
+      $(LD) --help 2>/dev/null | grep -q -- -dead_strip && echo '-Wl,-dead_strip';
       ;;
   esac
 endef
+
+# TIP: try add the'-Wl, --no-as-needed,-lrt' for ability to built with modern glibc, but then use with the old.
 define uname2libs
   case "$(UNAME)" in
     CYGWIN*|MINGW*|MSYS*|Windows*)
-      echo '-lm -lntdll -lwinmm'
+      echo '-lm -lntdll -lwinmm';
       ;;
     *SunOS*|*Solaris*)
-      echo '-lm -lkstat -lrt'
+      echo '-lm -lkstat -lrt';
       ;;
     *Darwin*|OpenBSD*)
-      echo '-lm'
+      echo '-lm';
       ;;
     *)
-      echo '-lm -lrt'
+      echo '-lm -lrt';
       ;;
   esac
 endef
+
 SO_SUFFIX  := $(shell $(uname2sosuffix))
 HEADERS    := mdbx.h mdbx.h++
 LIBRARIES  := libmdbx.a libmdbx.$(SO_SUFFIX)
@@ -161,7 +190,7 @@ show-options:
 	@echo "  CC       =`which $(CC)` | `$(CC) --version | head -1`"
 	@echo "  CFLAGS   =$(CFLAGS)"
 	@echo "  CXXFLAGS =$(CXXFLAGS)"
-	@echo "  LDFLAGS  =$(LDFLAGS) $(LIBS) $(EXE_LDFLAGS)"
+	@echo "  LDFLAGS  =$(LDFLAGS) $(LIB_STDCXXFS) $(LIBS) $(EXE_LDFLAGS)"
 	@echo '$(TIP) Use `make help` to listing available targets.'
 
 options: