diff --git a/lang/src/int_to_str.asm b/lang/src/int_to_str.asm
index ad86d71..a28fe73 100644
--- a/lang/src/int_to_str.asm
+++ b/lang/src/int_to_str.asm
@@ -5,24 +5,32 @@ global int_to_str2
 ;; rdi: input integer
 ;; rsi: pointer to output buffer (at least 21 bytes)
 ;; rdx: length of buffer
-;; fn int_to_str2(value: i64, buffer: *mut u8, len: usize) -> (*mut u8, usize)
+;; cl: radix
+;; fn int_to_str2(value: i64, buffer: *mut u8, len: usize, radix: u8) -> (*mut u8, usize)
 int_to_str2:
     push rbp
     mov rbp, rsp
     push r12
     push r13
-    xor r12, r12                ; r12 = index
-    mov r13, rdx                ; r13 = buffer length
+    sub rsp, 0x20
+    mov [rsp], rdi              ; save value
+    mov [rsp + 8], rdx          ; save length
+    mov [rsp + 16], rcx         ; save radix
 
-    test r13, r13
+    xor r12, r12                ; r12 = index
+
+    test rdx, rdx
     jz .epilogue                ; if length is 0, return
 
+    xor r13, r13
     mov rcx, rdi
     sar rcx, 63                 ; check sign
     cmp rcx, 0
     je .convert
 .negative:
     mov byte [rsi], '-'         ; write minus sign
+    neg rdi
+    inc r13
     inc r12
 
 .convert:
@@ -32,14 +40,22 @@ int_to_str2:
     jmp .epilogue
 
 .convert_loop:
-    cmp r12, r13
+    mov rax, [rsp + 8]          ; buffer length
+    cmp r12, rax
     jge .epilogue               ; prevent buffer overflow
 
     mov rax, rdi
     xor rdx, rdx
-    mov rcx, 10                 ; base 10
-    div rcx                     ; rax = rdi / 10, rdx = rdi % 10
+    mov rcx, [rsp + 16]         ; base 10
+    mov cl, cl
+    div rcx                     ; rax = rdi / radix, rdx = rdi % radix
+    cmp rdx, 10
+    jl .decimal
+    add rdx, 'a' - 10           ; convert to 'a'-'f'
+    jmp  .phi
+.decimal:
     add rdx, '0'                ; convert digit to ASCII
+.phi:
     mov byte [rsi + r12], dl
     inc r12
     mov rdi, rax
@@ -47,7 +63,6 @@ int_to_str2:
     jnz .convert_loop
 
     ; Reverse the digits
-    xor r13, r13
     mov rdx, r12
     dec r12                     ; last digit index
 .reverse_loop:
@@ -63,6 +78,7 @@ int_to_str2:
 .done_reverse:
     mov rax, rsi
 .epilogue:
+    add rsp, 0x20
     pop r13
     pop r12
     pop rbp
diff --git a/lang/tests/int_to_str.rs b/lang/tests/int_to_str.rs
index 0183ad0..0f3b73d 100644
--- a/lang/tests/int_to_str.rs
+++ b/lang/tests/int_to_str.rs
@@ -19,16 +19,37 @@ impl FFISlice {
 }
 
 unsafe extern "C" {
-    unsafe fn int_to_str2(value: usize, buffer: *mut u8, buffer_len: usize) -> FFISlice;
+    unsafe fn int_to_str2(value: isize, buffer: *mut u8, buffer_len: usize, radix: u8) -> FFISlice;
 }
 
 fn main() {
-    let value = 1234567890usize;
+    let value = 1234567890isize;
     let mut buffer = [0u8; 32];
     unsafe {
-        let slice = int_to_str2(value, buffer.as_mut_ptr(), buffer.len());
+        let slice = int_to_str2(value, buffer.as_mut_ptr(), buffer.len(), 10);
         let s = slice.as_str();
         println!("Integer: {}, String: {}", value, s);
-        assert_eq!(s, value.to_string());
+        assert_eq!(s, format!("{value}"));
+
+        let slice = int_to_str2(0 - value, buffer.as_mut_ptr(), buffer.len(), 10);
+        let s = slice.as_str();
+        println!("Integer: {}, String: {}", 0 - value, s);
+        assert_eq!(s, format!("{}", 0 - value));
+
+        let slice = int_to_str2(value, buffer.as_mut_ptr(), buffer.len(), 16);
+        let s = slice.as_str();
+        println!("Integer: {:x}, String: {}", value, s);
+        assert_eq!(s, format!("{value:x}"));
+
+        let slice = int_to_str2(value, buffer.as_mut_ptr(), buffer.len(), 8);
+        let s = slice.as_str();
+        println!("Integer: {:o}, String: {}", value, s);
+        assert_eq!(s, format!("{value:o}"));
+
+        let value = 235isize;
+        let slice = int_to_str2(value, buffer.as_mut_ptr(), buffer.len(), 2);
+        let s = slice.as_str();
+        println!("Integer: {:b}, String: {}", value, s);
+        assert_eq!(s, format!("{value:b}"));
     }
 }