--- a/GNUmakefile
+++ b/GNUmakefile
@@ -420,7 +420,7 @@ afl-as: src/afl-as.c include/afl-as.h $(COMM_HDR) | test_x86
 	@ln -sf afl-as as
 
 src/afl-performance.o : $(COMM_HDR) src/afl-performance.c include/hash.h
-	$(CC) $(CFLAGS) -Iinclude $(SPECIAL_PERFORMANCE) -O3 -fno-unroll-loops -c src/afl-performance.c -o src/afl-performance.o
+	$(CC) $(CFLAGS) -Iinclude $(SPECIAL_PERFORMANCE) -fno-unroll-loops -c src/afl-performance.c -o src/afl-performance.o
 
 src/afl-common.o : $(COMM_HDR) src/afl-common.c include/common.h
 	$(CC) $(CFLAGS) $(CFLAGS_FLTO) -c src/afl-common.c -o src/afl-common.o
--- a/GNUmakefile.gcc_plugin
+++ b/GNUmakefile.gcc_plugin
@@ -131,18 +131,18 @@ afl-common.o: ./src/afl-common.c
 	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@ $(LDFLAGS)
 
 ./afl-compiler-rt.o: instrumentation/afl-compiler-rt.o.c
-	$(CC) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -fPIC -c $< -o $@
+	$(CC) $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -fPIC -c $< -o $@
 
 ./afl-compiler-rt-32.o: instrumentation/afl-compiler-rt.o.c
 	@printf "[*] Building 32-bit variant of the runtime (-m32)... "
-	@$(CC) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -m32 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-32.o afl-llvm-rt-32.o; else echo "failed (that's fine)"; fi
+	@$(CC) $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -m32 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-32.o afl-llvm-rt-32.o; else echo "failed (that's fine)"; fi
 
 ./afl-compiler-rt-64.o: instrumentation/afl-compiler-rt.o.c
 	@printf "[*] Building 64-bit variant of the runtime (-m64)... "
-	@$(CC) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -m64 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-64.o afl-llvm-rt-64.o; else echo "failed (that's fine)"; fi
+	@$(CC) $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -m64 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-64.o afl-llvm-rt-64.o; else echo "failed (that's fine)"; fi
 
 ./afl-gcc-pass.so: instrumentation/afl-gcc-pass.so.cc | test_deps
-	$(CXX) $(CXXEFLAGS) $(PLUGIN_FLAGS) -shared $< -o $@
+	$(CXX) $(CXXEFLAGS) $(PLUGIN_FLAGS) -shared $< -o $@ $(LDFLAGS)
 	ln -sf afl-cc afl-gcc-fast
 	ln -sf afl-cc afl-g++-fast
 	ln -sf afl-cc.8 afl-gcc-fast.8
--- a/GNUmakefile.llvm
+++ b/GNUmakefile.llvm
@@ -438,20 +438,20 @@ afl-llvm-dict2file.so:	instrumentation/afl-llvm-dict2file.so.cc instrumentation/
 
 .PHONY: document
 document:
-	$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -O3 -Wno-unused-result -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt.o
-	@$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -O3 -Wno-unused-result -m32 -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt-32.o 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; else echo "failed (that's fine)"; fi
-	@$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -O3 -Wno-unused-result -m64 -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt-64.o 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; else echo "failed (that's fine)"; fi
+	$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -Wno-unused-result -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt.o
+	@$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -Wno-unused-result -m32 -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt-32.o 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; else echo "failed (that's fine)"; fi
+	@$(CLANG_BIN) -D_AFL_DOCUMENT_MUTATIONS $(CFLAGS) $(CFLAGS_SAFE) $(CPPFLAGS) $(CLANG_CFL) -Wno-unused-result -m64 -fPIC -c instrumentation/afl-compiler-rt.o.c -o ./afl-compiler-rt-64.o 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; else echo "failed (that's fine)"; fi
 
 ./afl-compiler-rt.o: instrumentation/afl-compiler-rt.o.c
-	$(CC) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -fPIC -c $< -o $@
+	$(CC) $(CFLAGS) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -fPIC -c $< -o $@
 
 ./afl-compiler-rt-32.o: instrumentation/afl-compiler-rt.o.c
 	@printf "[*] Building 32-bit variant of the runtime (-m32)... "
-	@$(CC) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -m32 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-32.o afl-llvm-rt-32.o; else echo "failed (that's fine)"; fi
+	@$(CC) $(CFLAGS) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -m32 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-32.o afl-llvm-rt-32.o; else echo "failed (that's fine)"; fi
 
 ./afl-compiler-rt-64.o: instrumentation/afl-compiler-rt.o.c
 	@printf "[*] Building 64-bit variant of the runtime (-m64)... "
-	@$(CC) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -O3 -Wno-unused-result -m64 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-64.o afl-llvm-rt-64.o; else echo "failed (that's fine)"; fi
+	@$(CC) $(CFLAGS) $(CLANG_CFL) $(CFLAGS_SAFE) $(CPPFLAGS) -Wno-unused-result -m64 -fPIC -c $< -o $@ 2>/dev/null; if [ "$$?" = "0" ]; then echo "success!"; ln -sf afl-compiler-rt-64.o afl-llvm-rt-64.o; else echo "failed (that's fine)"; fi
 
 .PHONY: test_build
 test_build: $(PROGS)
--- a/custom_mutators/honggfuzz/Makefile
+++ b/custom_mutators/honggfuzz/Makefile
@@ -1,5 +1,6 @@
 
-CFLAGS = -O3 -funroll-loops -fPIC -Wl,-Bsymbolic
+CFLAGS ?= -O3
+CFLAGS += -funroll-loops -fPIC -Wl,-Bsymbolic
 
 all: honggfuzz-mutator.so
 
--- a/custom_mutators/libfuzzer/Makefile
+++ b/custom_mutators/libfuzzer/Makefile
@@ -1,5 +1,6 @@
 
-CFLAGS = -g -O3 -funroll-loops -fPIC -fpermissive -std=c++11
+CFLAGS ?= -g -O3
+CFLAGS += -funroll-loops -fpermissive -std=c++11 -fPIC
 #CFLAGS = -g -O0 -fPIC -fpermissive -std=c++11
 CXX ?= clang++
 
--- a/frida_mode/GNUmakefile
+++ b/frida_mode/GNUmakefile
@@ -17,7 +17,6 @@ CFLAGS+=-fPIC \
 		-D_GNU_SOURCE \
 		-D_FORTIFY_SOURCE=2 \
 		-g \
-		-O3 \
 		-funroll-loops \
 		-ffunction-sections \
 
--- a/frida_mode/test/png/persistent/hook/GNUmakefile
+++ b/frida_mode/test/png/persistent/hook/GNUmakefile
@@ -5,11 +5,9 @@ BUILD_DIR:=$(PWD)build/
 AFLPP_FRIDA_DRIVER_HOOK_OBJ=$(ROOT)frida_mode/build/frida_hook.so
 AFLPP_QEMU_DRIVER_HOOK_OBJ=$(ROOT)frida_mode/build/qemu_hook.so
 
-CFLAGS+=-O3 \
-		-funroll-loops \
+CFLAGS+= -funroll-loops \
 		-g \
-		-fPIC \
-		-funroll-loops \
+		-fPIC
 
 LDFLAGS+=-shared \
 
--- a/utils/aflpp_driver/GNUmakefile
+++ b/utils/aflpp_driver/GNUmakefile
@@ -7,7 +7,7 @@ ifneq "" "$(LLVM_BINDIR)"
   LLVM_BINDIR := $(LLVM_BINDIR)/
 endif
 
-CFLAGS := -O3 -funroll-loops -g -fPIC
+CFLAGS ?= -O3 -funroll-loops -g -fPIC
 
 all:	libAFLDriver.a libAFLQemuDriver.a aflpp_qemu_driver_hook.so