diff --git a/math/catalan.c b/math/catalan.c
index 2116f5cb68..1539275acf 100644
--- a/math/catalan.c
+++ b/math/catalan.c
@@ -6,6 +6,8 @@ long int factorial(int x)  // long int for more than 10 factorial
 {
     int i;
     long int fac;  // fac stores x factorial
+    if (x == 0)
+        return 1;  // 0! = 1: without this factorial(0) = 0 and the formula divides by zero
     fac = x;
     for (i = 1; i < x; i++)  // loop to calculate x factorial
     {
@@ -19,6 +21,11 @@ int main()
     int n;
     float C;  // C is catalan number for n;
     scanf("%d", &n);
+    if (n < 0 || n > 10)
+    {
+        printf("n must be in [0, 10]: (2n)! overflows long int beyond that\n");
+        return 1;
+    }
     f1 = factorial(2 * n);
     f2 = factorial(n + 1);
     f3 = factorial(n);