diff --git a/build_lmer_table.c b/build_lmer_table.c
index 1502e69..48d536d 100644
--- a/build_lmer_table.c
+++ b/build_lmer_table.c
@@ -130,7 +130,7 @@ int main(int argc, char* argv[])
 int build_sequence(char *sequence, char *filename)
 {
   int i, j;
-  char c;
+  signed char c;
   FILE *fp;
 
   if( (fp = fopen(filename, "r")) == NULL)
diff --git a/build_repeat_families.c b/build_repeat_families.c
index 75d94ce..c8d5140 100644
--- a/build_repeat_families.c
+++ b/build_repeat_families.c
@@ -713,7 +713,7 @@ void print_parameters()
 int build_sequence(char *sequence, char *filename)
 {
   int i, j, seq;
-  char c;
+  signed char c;
   FILE *fp;
   int boundariesSize = 100;