diff --git a/src/util_m4ri.h b/src/util_m4ri.h
index afcfb16..173ca1d 100644
--- a/src/util_m4ri.h
+++ b/src/util_m4ri.h
@@ -214,6 +214,7 @@ static inline int nextelement(const word * const set1, const int m, const int po
   }
   else{
     w = SETWD(pos);
+    if (w >= m) return -1;
     setwd = set1[w] & (m4ri_ffff<< SETBT(pos));
   }
   for (;;){
diff --git a/src/utils.c b/src/utils.c
index 60388b9..156b7a4 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -77,7 +77,7 @@ FILE * nzlist_r_open(const char fnam[], long long int *lineno){
 #else /* treat signature line as comment */
   *lineno=1;
 #endif   
-  char c=fgetc(f); /** are there comments to skip? */  //  putchar(c);
+  int c=fgetc(f); /** are there comments to skip? */  //  putchar(c);
   while(c=='%'){ /** `comment line` starting with '%' */
     do{
       c=fgetc(f);      //      putchar(c);
@@ -106,7 +106,7 @@ one_vec_t * nzlist_r_one(FILE *f, one_vec_t * vec, const char fnam[], long long
     return NULL; /** not an actuall error */
   int w;
 
-  char c=fgetc(f); /** are there comments to skip? */
+  int c=fgetc(f); /** are there comments to skip? */
   while(c=='%'){ /** `comment line` starting with '%' */
     do{
       c=fgetc(f);