diff --git a/main-random-seq.c b/main-random-seq.c
index f8037fc..266ceb6 100644
--- a/main-random-seq.c
+++ b/main-random-seq.c
@@ -7,7 +7,7 @@
 int main(int argc, char **argv)
 {
     uint i, n, *pairs, *useq;
-    char *vienna;
+    char *vienna, *str;
 
     if (argc != 2 && argc != 3) {
         printf("ERROR: wrong number of arguments\n"
@@ -18,6 +18,7 @@ int main(int argc, char **argv)
     n = strlen(vienna);
     pairs = xmalloc(n * sizeof(*pairs));
     useq = xmalloc(n * sizeof(*useq));
+    str = xmalloc((n + 1) * sizeof(*str));
 
     if (argc == 3) {
         random_seed(atoi(argv[2]));
@@ -27,11 +28,10 @@ int main(int argc, char **argv)
 
     xvienna_to_pairs(n, vienna, pairs);
     random_useq(n, pairs, useq);
-    /* TODO: move this to useq_to_str function */
-    for (i = 0; i < n; i++)
-        printf("%c", NA_BASE_NAMES[useq[i]]);
-    printf("\n");
+    xuseq_to_str(n, useq, str);
+    printf("%s\n", str);
 
+    free(str);
     free(pairs);
     free(useq);
     return EXIT_SUCCESS;
diff --git a/na.c b/na.c
index b369e90..80fdcfd 100644
--- a/na.c
+++ b/na.c
@@ -244,6 +244,37 @@ xstr_to_pseq(uint n, uint ndim, const char *str, double **p)
     }
 }
 
+/* translate from uint sequence representation to string, exiting on
+   errors */
+void
+xuseq_to_str(uint n, const uint *useq, char *str)
+{
+    bool verbose = true;
+    int retcode = useq_to_str(n, useq, verbose, str);
+    if (retcode != EXIT_SUCCESS) {
+        exit(EXIT_FAILURE);
+    }
+}
+
+/* translate from uint sequence representation to string, return
+   EXIT_SUCCESS on success */
+int
+useq_to_str(uint n, const uint *useq, bool verbose, char *str)
+{
+    uint i;
+    str[n] = '\0';
+    for (i = 0; i < n; i++) {
+        if (useq[i] >= NA_NBASES) {
+            if (verbose) {
+                printf("ERROR: illegal base at position %u, base id = %u\n", i, useq[i]);
+            }
+            return EXIT_FAILURE;
+        }
+        str[i] = NA_BASE_NAMES[useq[i]];
+    }
+    return EXIT_SUCCESS;
+}
+
 void
 nn_multiloop_xalloc(struct nn_multiloop *ml, uint nstems, uint ndangle5,
                     uint ndangle3)
diff --git a/na.h b/na.h
index 24b9ebe..8bd8814 100644
--- a/na.h
+++ b/na.h
@@ -68,6 +68,8 @@ char *   xpairs_to_vienna(uint n, const uint *pairs, char *vienna);
 void     xstr_to_useq(uint n, const char *str, uint *useq);
 void     xstr_to_pseq(uint n, uint ndim, const char *str, double **p);
 void     pseq_to_str(double **p, uint n, uint ndim, char *str);
+void     xuseq_to_str(uint n, const uint *useq, char *str);
+int      useq_to_str(uint n, const uint *useq, bool verbose, char *str);
 
 struct nn_inter *  nn_inter_xnew(uint n);
 void               nn_inter_delete(struct nn_inter *inter);