Unexpected error in C inline function

Question

I am trying to write a function returning the maximum value between two integers. The below code gives an error message when I run it on repl.it. But when I remove "inline", it becomes normal. Why am I doing wrong? Thanks!

#include <stdio.h>

inline int max(int a, int b){
  return (a>b)? a: b;
}

int main( ) {
  int a = 3, b = 4;
  int c = max(a,b);
  printf("%d", c);
  return 0;
}