diff --git a/makefile.basic b/makefile.basic
index 9caa392..ae37bb5 100644
--- a/makefile.basic
+++ b/makefile.basic
@@ -23,7 +23,7 @@ SOURCE_DIRS::=src
 SOURCES::=
 OBJDIR::=obj
 DEPDIR::=$(OBJDIR)/dep
-LIBDIRS::=
+LIBDIRS::=lib
 INCLUDE_DIRS::=include
 CFLAGS::=-std=c18 -Wall -pedantic -Wextra
 CXXFLAGS::=-std=c++17 -Wall -pedantic -Wextra
@@ -32,6 +32,7 @@ LANG::=$(EXT)
 MAIN_EXECUTABLE::=tester
 RELEASE?=0
 MEMCHK?=0
+UNDEFCHK?=0
 SAVEFLAGS?=1
 
 ifneq ($(WINDOWS),1)
@@ -107,16 +108,20 @@ endif
 
 
 ifeq ($(RELEASE),1)
-#a lot of false strict aliasing warnings from gcc 9
-COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
-
-else ifeq ($(MEMCHK),1)
-	#use asan to check memory leaks/invalid accesses
-	LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
-	COMPILER_FLAGS+=-O0 -g3 -ggdb -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	#a lot of false strict aliasing warnings from gcc 9
+	COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
 else
 	#default target
 	COMPILER_FLAGS+=-O0 -g3 -ggdb
+	ifeq ($(MEMCHK),1)
+		#use asan to check memory leaks/invalid accesses
+		LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+		COMPILER_FLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	endif
+	ifeq ($(UNDEFCHK),1)
+		LDFLAGS+=-fsanitize=undefined
+		COMPILER_FLAGS+=-fsanitize=undefined
+	endif
 endif
 
 ifeq ($(SAVEFLAGS),1)
diff --git a/makefile.exe_progress b/makefile.exe_progress
index ad695de..7c6e398 100644
--- a/makefile.exe_progress
+++ b/makefile.exe_progress
@@ -35,6 +35,7 @@ POST_TARGETS::=
 CLEAN_TARGETS::=
 RELEASE?=0
 MEMCHK?=0
+UNDEFCHK?=0
 SAVECFLAGS?=1
 VERBOSE=0
 
@@ -106,13 +107,18 @@ ifeq ($(RELEASE),1)
 	#a lot of false strict aliasing warnings from gcc 9
 	COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
 	POST_TARGETS+= do_strip
-else ifeq ($(MEMCHK),1)
-	#use asan to check memory leaks/invalid accesses
-	LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
-	COMPILER_FLAGS+=-O0 -g3 -ggdb -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
 else
 	#default target
 	COMPILER_FLAGS+=-O0 -g3 -ggdb
+	ifeq ($(MEMCHK),1)
+		#use asan to check memory leaks/invalid accesses
+		LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+		COMPILER_FLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	endif
+	ifeq ($(UNDEFCHK),1)
+		LDFLAGS+=-fsanitize=undefined
+		COMPILER_FLAGS+=-fsanitize=undefined
+	endif
 endif
 
 ifeq ($(SAVECFLAGS),1)
diff --git a/makefile.library b/makefile.library
index 53a6a3f..17e8743 100644
--- a/makefile.library
+++ b/makefile.library
@@ -34,6 +34,7 @@ SHARED?=1
 STATIC?=0
 RELEASE?=0
 MEMCHK?=0
+UNDEFCHK?=0
 SAVEFLAGS?=1
 
 ifneq ($(WINDOWS),1)
@@ -121,13 +122,18 @@ endif
 ifeq ($(RELEASE),1)
 	#a lot of false strict aliasing warnings from gcc 9
 	COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
-else ifeq ($(MEMCHK),1)
-	#use asan to check memory leaks/invalid accesses
-	LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
-	COMPILER_FLAGS+=-O0 -g3 -ggdb -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
 else
 	#default target
 	COMPILER_FLAGS+=-O0 -g3 -ggdb
+	ifeq ($(MEMCHK),1)
+		#use asan to check memory leaks/invalid accesses
+		LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+		COMPILER_FLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	endif
+	ifeq ($(UNDEFCHK),1)
+		LDFLAGS+=-fsanitize=undefined
+		COMPILER_FLAGS+=-fsanitize=undefined
+	endif
 endif
 
 ifeq ($(SAVEFLAGS),1)
diff --git a/makefile.reclib b/makefile.reclib
index 76fc10e..576efda 100644
--- a/makefile.reclib
+++ b/makefile.reclib
@@ -37,6 +37,7 @@ SHARED?=1
 STATIC?=0
 RELEASE?=0
 MEMCHK?=0
+UNDEFCHK?=0
 SAVEFLAGS?=1
 
 ifneq ($(WINDOWS),1)
@@ -114,13 +115,18 @@ ifeq ($(RELEASE),1)
 	#a lot of false strict aliasing warnings from gcc 9
 	COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
 	POST_TARGETS+= do_strip
-else ifeq ($(MEMCHK),1)
-	#use asan to check memory leaks/invalid accesses
-	LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
-	COMPILER_FLAGS+=-O0 -g3 -ggdb -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
 else
 	#default target
 	COMPILER_FLAGS+=-O0 -g3 -ggdb
+	ifeq ($(MEMCHK),1)
+		#use asan to check memory leaks/invalid accesses
+		LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+		COMPILER_FLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	endif
+	ifeq ($(UNDEFCHK),1)
+		LDFLAGS+=-fsanitize=undefined
+		COMPILER_FLAGS+=-fsanitize=undefined
+	endif
 endif
 
 ifeq ($(SAVEFLAGS),1)
diff --git a/makefile.recursive b/makefile.recursive
index b0e47b7..ce2363c 100644
--- a/makefile.recursive
+++ b/makefile.recursive
@@ -35,6 +35,7 @@ POST_TARGETS::=
 CLEAN_TARGETS::=
 RELEASE?=0
 MEMCHK?=0
+UNDEFCHK?=0
 SAVEFLAGS?=1
 
 ifneq ($(WINDOWS),1)
@@ -105,13 +106,18 @@ endif
 ifeq ($(RELEASE),1)
 	#a lot of false strict aliasing warnings from gcc 9
 	COMPILER_FLAGS+=-O2 -Wno-strict-aliasing
-else ifeq ($(MEMCHK),1)
-	#use asan to check memory leaks/invalid accesses
-	LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
-	COMPILER_FLAGS+=-O0 -g3 -ggdb -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
 else
 	#default target
 	COMPILER_FLAGS+=-O0 -g3 -ggdb
+	ifeq ($(MEMCHK),1)
+		#use asan to check memory leaks/invalid accesses
+		LDFLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+		COMPILER_FLAGS+=-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls
+	endif
+	ifeq ($(UNDEFCHK),1)
+		LDFLAGS+=-fsanitize=undefined
+		COMPILER_FLAGS+=-fsanitize=undefined
+	endif
 endif
 
 ifeq ($(SAVEFLAGS),1)