From a70770ecef11ce40eefb87a074a4e1cf7e81d51c Mon Sep 17 00:00:00 2001
From: Andreas Untergasser <andreas@untergasser.de>
Date: Wed, 25 Sep 2024 20:37:00 +0200
Subject: [PATCH] Fix not allowing negative positions after first index
 correction

---
 src/libprimer3.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/libprimer3.cc b/src/libprimer3.cc
index 54a13f9..7da003d 100644
--- a/src/libprimer3.cc
+++ b/src/libprimer3.cc
@@ -7783,9 +7783,12 @@ _check_and_adjust_1_interval(const char *tag_name,
       pr_append(err, " illegal interval");
       return 1;
     }
-    intervals[i][0] -= first_index;
+    if (intervals[i][0] - first_index > 0) {
+      intervals[i][0] -= first_index;
+    } else {
+      intervals[i][0] = 0;
+    }
   }
-
   for (i=0; i < num_intervals; i++) {
     if (empty_allowed && (intervals[i][0] == -1) && (intervals[i][1] == -1))
       continue;