diff --git a/lib/c.c b/lib/c.c
index 7ec2dbb8..0c2ff7bb 100644
--- a/lib/c.c
+++ b/lib/c.c
@@ -45,7 +45,7 @@
 
 typedef int FILE;
 
-void abort();
+void abort(void);
 
 int strlen(char *str)
 {
@@ -458,7 +458,7 @@ int snprintf(char *buffer, int n, char *str, ...)
     return fmtbuf.len;
 }
 
-int __free_all();
+int __free_all(void);
 
 void exit(int exit_code)
 {
@@ -466,7 +466,7 @@ void exit(int exit_code)
     __syscall(__syscall_exit, exit_code);
 }
 
-void abort()
+void abort(void)
 {
     printf("Abnormal program termination\n");
     exit(-1);
@@ -698,7 +698,7 @@ void __rfree(void *ptr, int size)
     __syscall(__syscall_munmap, ptr, size);
 }
 
-int __free_all()
+int __free_all(void)
 {
     if (!__freelist_head && !__alloc_head)
         return 0;
diff --git a/src/arm-codegen.c b/src/arm-codegen.c
index 1f624f2b..ded8b0cd 100644
--- a/src/arm-codegen.c
+++ b/src/arm-codegen.c
@@ -130,7 +130,7 @@ void update_elf_offset(ph2_ir_t *ph2_ir)
     }
 }
 
-void cfg_flatten()
+void cfg_flatten(void)
 {
     func_t *func = find_func("__syscall");
     func->bbs->elf_offset = 44; /* offset of start + exit in codegen */
@@ -447,7 +447,7 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
     }
 }
 
-void code_generate()
+void code_generate(void)
 {
     elf_data_start = elf_code_start + elf_offset;
 
diff --git a/src/arm.c b/src/arm.c
index 4271cbf6..3fae60b7 100644
--- a/src/arm.c
+++ b/src/arm.c
@@ -126,7 +126,7 @@ int arm_encode(arm_cond_t cond, int opcode, int rn, int rd, int op2)
     return (cond << 28) + (opcode << 20) + (rn << 16) + (rd << 12) + op2;
 }
 
-int __svc()
+int __svc(void)
 {
     return arm_encode(__AL, 240, 0, 0, 0);
 }
diff --git a/src/elf.c b/src/elf.c
index deed1d9d..d17c324e 100644
--- a/src/elf.c
+++ b/src/elf.c
@@ -47,7 +47,7 @@ void elf_write_blk(strbuf_t *elf_array, void *blk, int sz)
         strbuf_putc(elf_array, ptr[i]);
 }
 
-void elf_generate_header()
+void elf_generate_header(void)
 {
     elf32_hdr_t hdr;
     /*
@@ -173,7 +173,7 @@ void elf_generate_header()
     elf_write_blk(elf_header, &phdr, sizeof(elf32_phdr_t));
 }
 
-void elf_generate_sections()
+void elf_generate_sections(void)
 {
     /* symtab section */
     for (int b = 0; b < elf_symtab->size; b++)
@@ -310,7 +310,7 @@ void elf_generate_sections()
     elf_write_blk(elf_section, &shdr, sizeof(elf32_shdr_t));
 }
 
-void elf_align()
+void elf_align(void)
 {
     while (elf_data->size & 3)
         elf_write_byte(elf_data, 0);
diff --git a/src/globals.c b/src/globals.c
index b861103e..7e200bfa 100644
--- a/src/globals.c
+++ b/src/globals.c
@@ -600,7 +600,7 @@ int find_macro_param_src_idx(char *name, block_t *parent)
     return 0;
 }
 
-type_t *add_type()
+type_t *add_type(void)
 {
     return &TYPES[types_idx++];
 }
@@ -970,7 +970,7 @@ void strbuf_free(strbuf_t *src)
 /* This routine is required because the global variable initializations are
  * not supported now.
  */
-void global_init()
+void global_init(void)
 {
     elf_code_start = ELF_START + elf_header_len;
 
@@ -994,7 +994,7 @@ void global_init()
     elf_section = strbuf_create(MAX_SECTION);
 }
 
-void global_release()
+void global_release(void)
 {
     free(MACROS);
     free(TYPES);
@@ -1286,7 +1286,7 @@ void dump_bb_insn_by_dom(func_t *func, basic_block_t *bb, bool *at_func_start)
     }
 }
 
-void dump_insn()
+void dump_insn(void)
 {
     printf("==<START OF INSN DUMP>==\n");
 
diff --git a/src/lexer.c b/src/lexer.c
index 8064d1e8..e2854f34 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -63,7 +63,7 @@ bool is_numeric(char buffer[])
     return true;
 }
 
-void skip_whitespace()
+void skip_whitespace(void)
 {
     while (true) {
         if (is_linebreak(next_char)) {
@@ -533,13 +533,13 @@ token_t lex_token_internal(bool aliasing)
 /* Lex next token and returns its token type. To disable aliasing on next
  * token, use 'lex_token_internal'.
  */
-token_t lex_token()
+token_t lex_token(void)
 {
     return lex_token_internal(true);
 }
 
 /* Skip the content. We only need the index where the macro body begins. */
-void skip_macro_body()
+void skip_macro_body(void)
 {
     while (!is_newline(next_char))
         next_token = lex_token();
diff --git a/src/parser.c b/src/parser.c
index 42b97087..47314578 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -108,7 +108,7 @@ void opstack_push(var_t *var)
     operand_stack[operand_stack_idx++] = var;
 }
 
-var_t *opstack_pop()
+var_t *opstack_pop(void)
 {
     return operand_stack[--operand_stack_idx];
 }
@@ -179,7 +179,7 @@ int get_unary_operator_prio(opcode_t op)
     }
 }
 
-opcode_t get_operator()
+opcode_t get_operator(void)
 {
     opcode_t op = OP_generic;
     if (lex_accept(T_plus))
@@ -317,7 +317,7 @@ int read_numeric_constant(char buffer[])
     return value;
 }
 
-int read_constant_expr_operand()
+int read_constant_expr_operand(void)
 {
     char buffer[MAX_ID_LEN];
     int value;
@@ -449,7 +449,7 @@ int read_constant_infix_expr(int precedence)
     return lhs;
 }
 
-int read_constant_expr()
+int read_constant_expr(void)
 {
     return read_constant_infix_expr(0);
 }
@@ -457,7 +457,7 @@ int read_constant_expr()
 /* Skips lines where preprocessor match is false, this will stop once next
  * token is either 'T_cppd_elif', 'T_cppd_else' or 'cppd_endif'.
  */
-void cppd_control_flow_skip_lines()
+void cppd_control_flow_skip_lines(void)
 {
     while (!lex_peek(T_cppd_elif, NULL) && !lex_peek(T_cppd_else, NULL) &&
            !lex_peek(T_cppd_endif, NULL)) {
@@ -472,7 +472,7 @@ void check_def(char *alias, bool expected)
         preproc_match = true;
 }
 
-void read_defined_macro()
+void read_defined_macro(void)
 {
     char lookup_alias[MAX_TOKEN_LEN];
 
@@ -487,7 +487,7 @@ void read_defined_macro()
 /* read preprocessor directive at each potential positions: e.g.,
  * global statement / body statement
  */
-bool read_preproc_directive()
+bool read_preproc_directive(void)
 {
     char token[MAX_ID_LEN];
 
@@ -728,6 +728,21 @@ void read_parameter_list_decl(func_t *func, int anon)
 {
     int vn = 0;
     lex_expect(T_open_bracket);
+
+    char token[MAX_TYPE_LEN];
+    if (lex_peek(T_identifier, token) && !strncmp(token, "void", 4)) {
+        next_token = lex_token();
+        if (lex_accept(T_close_bracket))
+            return;
+        func->param_defs[vn].type = TY_void;
+        read_inner_var_decl(&func->param_defs[vn], anon, 1);
+        if (!func->param_defs[vn].is_ptr && !func->param_defs[vn].is_func &&
+            !func->param_defs[vn].array_size)
+            error("'void' must be the only parameter and unnamed");
+        vn++;
+        lex_accept(T_comma);
+    }
+
     while (lex_peek(T_identifier, NULL) == 1) {
         read_full_var_decl(&func->param_defs[vn++], anon, 1);
         lex_accept(T_comma);
@@ -1954,7 +1969,7 @@ bool read_body_assignment(char *token,
     return false;
 }
 
-int read_primary_constant()
+int read_primary_constant(void)
 {
     /* return signed constant */
     int isneg = 0, res;
@@ -2819,7 +2834,7 @@ void read_global_decl(block_t *block)
     error("Syntax error in global declaration");
 }
 
-void read_global_statement()
+void read_global_statement(void)
 {
     char token[MAX_ID_LEN];
     block_t *block = GLOBAL_BLOCK; /* global block */
@@ -2938,7 +2953,7 @@ void read_global_statement()
         error("Syntax error in global statement");
 }
 
-void parse_internal()
+void parse_internal(void)
 {
     /* set starting point of global stack manually */
     GLOBAL_FUNC = add_func("", true);
diff --git a/src/peephole.c b/src/peephole.c
index 80a3074b..aca6ca7a 100644
--- a/src/peephole.c
+++ b/src/peephole.c
@@ -146,7 +146,7 @@ bool insn_fusion(ph2_ir_t *ph2_ir)
     return false;
 }
 
-void peephole()
+void peephole(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         for (basic_block_t *bb = func->bbs; bb; bb = bb->rpo_next) {
diff --git a/src/reg-alloc.c b/src/reg-alloc.c
index d130a21b..f60c5c00 100644
--- a/src/reg-alloc.c
+++ b/src/reg-alloc.c
@@ -240,7 +240,7 @@ void extend_liveness(basic_block_t *bb, insn_t *insn, var_t *var, int offset)
         var->consumed = insn->idx + offset;
 }
 
-void reg_alloc()
+void reg_alloc(void)
 {
     /* TODO: .bss and .data section */
     for (insn_t *global_insn = GLOBAL_FUNC->bbs->insn_list.head; global_insn;
@@ -649,7 +649,7 @@ void reg_alloc()
     }
 }
 
-void dump_ph2_ir()
+void dump_ph2_ir(void)
 {
     for (int i = 0; i < ph2_ir_idx; i++) {
         ph2_ir_t *ph2_ir = PH2_IR_FLATTEN[i];
diff --git a/src/riscv-codegen.c b/src/riscv-codegen.c
index db5f1824..27df288b 100644
--- a/src/riscv-codegen.c
+++ b/src/riscv-codegen.c
@@ -104,7 +104,7 @@ void update_elf_offset(ph2_ir_t *ph2_ir)
     }
 }
 
-void cfg_flatten()
+void cfg_flatten(void)
 {
     func_t *func = find_func("__syscall");
     func->bbs->elf_offset = 48; /* offset of start + exit in codegen */
@@ -426,7 +426,7 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
     }
 }
 
-void code_generate()
+void code_generate(void)
 {
     elf_data_start = elf_code_start + elf_offset;
 
diff --git a/src/riscv.c b/src/riscv.c
index da1b861f..3ea8b57e 100644
--- a/src/riscv.c
+++ b/src/riscv.c
@@ -372,17 +372,17 @@ int __auipc(rv_reg rd, int imm)
     return rv_encode_U(rv_auipc, rd, imm);
 }
 
-int __ecall()
+int __ecall(void)
 {
     return rv_encode_I(rv_ecall, __zero, __zero, 0);
 }
 
-int __ebreak()
+int __ebreak(void)
 {
     return rv_encode_I(rv_ebreak, __zero, __zero, 1);
 }
 
-int __nop()
+int __nop(void)
 {
     return __addi(__zero, __zero, 0);
 }
diff --git a/src/ssa.c b/src/ssa.c
index 62d97a29..cdbee2d8 100644
--- a/src/ssa.c
+++ b/src/ssa.c
@@ -102,7 +102,7 @@ void bb_build_rpo(func_t *func, basic_block_t *bb)
     prev->rpo_next = bb;
 }
 
-void build_rpo()
+void build_rpo(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -146,7 +146,7 @@ basic_block_t *intersect(basic_block_t *i, basic_block_t *j)
  *   Cooper, Keith D.; Harvey, Timothy J.; Kennedy, Ken (2001).
  *   "A Simple, Fast Dominance Algorithm"
  */
-void build_idom()
+void build_idom(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         bool changed;
@@ -219,7 +219,7 @@ void bb_build_dom(func_t *func, basic_block_t *bb)
     }
 }
 
-void build_dom()
+void build_dom(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -254,7 +254,7 @@ void bb_build_df(func_t *func, basic_block_t *bb)
     }
 }
 
-void build_df()
+void build_df(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -279,7 +279,7 @@ basic_block_t *reverse_intersect(basic_block_t *i, basic_block_t *j)
     return i;
 }
 
-void build_r_idom()
+void build_r_idom(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         bool changed;
@@ -349,7 +349,7 @@ void bb_build_rdom(func_t *func, basic_block_t *bb)
     }
 }
 
-void build_rdom()
+void build_rdom(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -394,7 +394,7 @@ void bb_build_rdf(func_t *func, basic_block_t *bb)
     }
 }
 
-void build_rdf()
+void build_rdf(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -442,7 +442,7 @@ void use_chain_delete(use_chain_t *u, var_t *var)
     free(u);
 }
 
-void use_chain_build()
+void use_chain_build(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         for (basic_block_t *bb = func->bbs; bb; bb = bb->rpo_next) {
@@ -547,7 +547,7 @@ void bb_solve_globals(func_t *func, basic_block_t *bb)
     }
 }
 
-void solve_globals()
+void solve_globals(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -610,7 +610,7 @@ bool insert_phi_insn(basic_block_t *bb, var_t *var)
     return true;
 }
 
-void solve_phi_insertion()
+void solve_phi_insertion(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         for (symbol_t *sym = func->global_sym_list.head; sym; sym = sym->next) {
@@ -794,7 +794,7 @@ void bb_solve_phi_params(basic_block_t *bb)
     }
 }
 
-void solve_phi_params()
+void solve_phi_params(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         for (int i = 0; i < func->num_params; i++) {
@@ -866,7 +866,7 @@ void bb_unwind_phi(func_t *func, basic_block_t *bb)
         insn->prev = NULL;
 }
 
-void unwind_phi()
+void unwind_phi(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -1212,7 +1212,7 @@ void dump_dom(char name[])
 }
 #endif
 
-void ssa_build()
+void ssa_build(void)
 {
     build_rpo();
     build_idom();
@@ -1499,7 +1499,7 @@ void dce_insn(basic_block_t *bb)
     }
 }
 
-void dce_sweep()
+void dce_sweep(void)
 {
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
         for (basic_block_t *bb = func->bbs; bb; bb = bb->rpo_next) {
@@ -1540,7 +1540,7 @@ void dce_sweep()
 
 void build_reversed_rpo();
 
-void optimize()
+void optimize(void)
 {
     /* build rdf information for DCE */
     build_reversed_rpo();
@@ -1607,7 +1607,7 @@ void bb_build_reversed_rpo(func_t *func, basic_block_t *bb)
     prev->rpo_r_next = bb;
 }
 
-void build_reversed_rpo()
+void build_reversed_rpo(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
@@ -1757,7 +1757,7 @@ bool recompute_live_out(basic_block_t *bb)
     return false;
 }
 
-void liveness_analysis()
+void liveness_analysis(void)
 {
     bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
     for (func_t *func = FUNC_LIST.head; func; func = func->next) {
diff --git a/tests/driver.sh b/tests/driver.sh
index b01400bb..9b35a317 100755
--- a/tests/driver.sh
+++ b/tests/driver.sh
@@ -267,6 +267,12 @@ int main() { return 0; }
 EOF
 
 # functions
+try_ 0 << EOF
+int main(void) {
+    return 0;
+}
+EOF
+
 try_ 55 << EOF
 int sum(int m, int n) {
     int acc;
@@ -319,6 +325,14 @@ int main() {
 }
 EOF
 
+try_compile_error << EOF
+int main(void v) {}
+EOF
+
+try_compile_error << EOF
+int main(void, int i) {}
+EOF
+
 # Unreachable declaration should not cause prog seg-falut (prog should leave normally with exit code 0)
 try_ 0 << EOF
 int main()