diff --git a/du6/program.c b/du6/program.c
index 2660a36..53a879f 100644
--- a/du6/program.c
+++ b/du6/program.c
@@ -14,7 +14,7 @@ int main(){
     for(int i = 0; fgets(inputs[i], 50, stdin) != NULL; i++){
         if(i == 0){
             freePlaces = (int) strtol(inputs[0], &ptr, 10);
-            if(freePlaces < 0 || !isdigit(freePlaces)){
+            if(freePlaces < 0 || !isdigit(freePlaces+'0')){
                 printf("Nespravny vstup %d\n", freePlaces);
             }
         }