diff --git a/src/lib/src/fwts_fileio.c b/src/lib/src/fwts_fileio.c
index c0a6f15..66e399f 100644
--- a/src/lib/src/fwts_fileio.c
+++ b/src/lib/src/fwts_fileio.c
@@ -37,7 +37,7 @@ fwts_list *fwts_file_read(FILE *fp)
 		return NULL;
 
 	while (fgets(buffer, sizeof(buffer), fp) != NULL) {
-		int len = strlen(buffer);
+		size_t len = strlen(buffer);
 		buffer[len-1] = '\0';	/* Chop off "\n" */
 		fwts_text_list_append(list, buffer);
 	}