diff --git a/README.md b/README.md
index 8bc9689..9d0ca31 100644
--- a/README.md
+++ b/README.md
@@ -129,7 +129,7 @@ sudo apt install gcc-riscv64-linux-gnu g++-riscv64-linux-gnu qemu-user-static
 
 ```sh
 # Compile C source code into RISC-V assembly
-riscv64-linux-gnu-gcc hello.c -S -o hello.S
+riscv64-linux-gnu-gcc hello.c -S -fsigned-char -o hello.S
 
 # Link to an RISC-V executable
 riscv64-linux-gnu-gcc -static hello.S -o hello
diff --git a/bench/Makefile b/bench/Makefile
index 0ecbacd..4c76581 100644
--- a/bench/Makefile
+++ b/bench/Makefile
@@ -23,13 +23,13 @@ run-gcc: bench-gcc
 	qemu-riscv64-static -L /usr/riscv64-linux-gnu ./bench-gcc
 
 driver.o: $(SRCS) driver.cpp
-	$(CXX) $(CFLAGS) -o driver.o -c -I. driver.cpp
+	$(CXX) $(CFLAGS) -fsigned-char -o driver.o -c -I. driver.cpp
 
 .c.s: $(KECC)
 	($(KECC) -O $< >$@) || (rm $@ -rf; exit 1)
 
 .c.o:
-	($(CC) -O -c $< -o $@) || (rm $@ -rf; exit 1)
+	($(CC) -O -fsigned-char -c $< -o $@) || (rm $@ -rf; exit 1)
 
 $(KECC):
 	cargo build --manifest-path=../Cargo.toml --release --bin kecc