diff -up INCHI-1-SRC/INCHI_API/demos/inchi_main/gcc/makefile.r INCHI-1-SRC/INCHI_API/demos/inchi_main/gcc/makefile
--- INCHI-1-SRC/INCHI_API/demos/inchi_main/gcc/makefile.r	2019-06-22 20:25:28.000000000 +0200
+++ INCHI-1-SRC/INCHI_API/demos/inchi_main/gcc/makefile	2020-10-13 14:18:22.809829859 +0200
@@ -30,7 +30,7 @@ INCHI_LIB_PATHNAME = $(LIB_DIR)/$(INCHI_
 # === Main program name ====
 ifndef API_CALLER_NAME
   ifndef CALLER_IS_MOL2INCHI 
-  API_CALLER_NAME = inchi_main$
+  API_CALLER_NAME = inchi_main
   else
   API_CALLER_NAME = mol2inchi$
   endif
@@ -43,9 +43,9 @@ endif
 # === Linker to create Main program =====
 ifndef LINKER
   ifdef ISLINUX
-	 LINKER_CWD_PATH = -Wl,-R,""
+	 LINKER_CWD_PATH =
   endif
-  LINKER = gcc -s $(LINKER_CWD_PATH)
+  LINKER = gcc $(LINKER_CWD_PATH)
 endif
 ifndef P_LIBR
 	P_LIBR = ../../../libinchi/src/
@@ -70,7 +70,7 @@ endif
 # === C Compiler Options =======
 ifndef C_OPTIONS
   ifndef CALLER_IS_MOL2INCHI
-	C_OPTIONS = -ansi -O3 -c
+	C_OPTIONS = -ansi $(OPTFLAGS) -c
   else
 	C_OPTIONS = -O3 -c  
   endif
diff -up INCHI-1-SRC/INCHI_EXE/inchi-1/gcc/makefile.r INCHI-1-SRC/INCHI_EXE/inchi-1/gcc/makefile
--- INCHI-1-SRC/INCHI_EXE/inchi-1/gcc/makefile.r	2016-09-08 19:08:16.000000000 +0200
+++ INCHI-1-SRC/INCHI_EXE/inchi-1/gcc/makefile	2020-10-13 14:18:22.809829859 +0200
@@ -13,7 +13,7 @@ ifndef CPP_COMPILER
 	CPP_COMPILER = g++
 endif
 ifndef LINKER
-	LINKER = g++ -s
+	LINKER = gcc
 endif
 ifndef INCHI_EXECUTABLE_NAME
 	ifdef windir
@@ -36,7 +36,7 @@ ifndef P_BASE
 endif
 #P_INCL = -I$(P_MAIN) -I$(P_BASE)
 P_INCL = -I$(P_MAIN) -I$(P_BASE)
-C_COMPILER_OPTIONS = $(P_INCL) -ansi -DCOMPILE_ANSI_ONLY -DTARGET_EXE_STANDALONE -O3 -c
+C_COMPILER_OPTIONS = $(P_INCL) -ansi -DCOMPILE_ANSI_ONLY -DTARGET_EXE_STANDALONE $(OPTFLAGS) -c
 #C_COMPILER_OPTIONS = -c $(P_INCL) -ansi -O3 -fsigned-char -ffunction-sections -fexpensive-optimizations -fstack-check -fexceptions -Wall -pedantic -Wbad-function-cast -Wreturn-type -Wformat -Wuninitialized -Wcast-align -Wshadow -Wunused -Wunused-value -Wunused-variable -Wunused-function -Wunused-parameter -Wunused-label -Wcomment -Wcast-qual -Wconversion -Wimplicit-int -Wmissing-braces -Wmissing-declarations -Wmissing-prototypes -Wredundant-decls -Wsign-compare -Wfloat-equal -Wstrict-prototypes -Wwrite-strings -Wundef -Waggregate-return -Wchar-subscripts -Wformat-nonliteral -Wnested-externs -Wsequence-point -Wpointer-arith -mfancy-math-387 -mieee-fp -mno-soft-float
 ifdef windir
 # no -ansi option due to reported MinGw bug