diff --git a/smenu.c b/smenu.c
index 5f0230d..86234c6 100644
--- a/smenu.c
+++ b/smenu.c
@@ -849,6 +849,20 @@ beep(toggle_t * toggle)
   }
 }
 
+/* ========================================== */
+/* Integer verification constraint for ctxopt */
+/* ========================================== */
+int
+check_integer_constraint(int nb_args, char ** args, char * value, char * par)
+{
+  if (!is_integer(value))
+  {
+    fprintf(stderr, "This argument of %s is not an integer: %s", par, value);
+    return 0;
+  }
+  return 1;
+}
+
 /* ======================================================================== */
 /* Update the bitmap associated with a word. This bitmap indicates the      */
 /* positions of the UFT-8 glyphs of the search buffer in each word.         */
@@ -6413,7 +6427,7 @@ main(int argc, char * argv[])
                           "[^:]+:.+");
   ctxopt_add_opt_settings(constraints, "da_options", ctxopt_re_constraint,
                           "[^:]+:.+");
-  ctxopt_add_opt_settings(constraints, "lines", ctxopt_format_constraint, "%u");
+  ctxopt_add_opt_settings(constraints, "lines", check_integer_constraint, "");
 
   ctxopt_add_opt_settings(constraints, "tab_mode", ctxopt_format_constraint,
                           "%ld");
diff --git a/smenu.h b/smenu.h
index a39700e..9f50787 100644
--- a/smenu.h
+++ b/smenu.h
@@ -215,6 +215,9 @@ void
 disp_message(ll_t * message_lines_list, long width, long max_len, term_t * term,
              win_t * win);
 
+int
+check_integer_constraint(int nb_args, char ** args, char * value, char * par);
+
 void
 update_bitmaps(search_mode_t search_mode, search_data_t * search_data,
                bitmap_affinity_t affinity);
diff --git a/utils.c b/utils.c
index 7309d80..2d74cdb 100644
--- a/utils.c
+++ b/utils.c
@@ -302,3 +302,18 @@ xwcscasecmp(const wchar_t * s1, const wchar_t * s2)
   }
   return (-*s2);
 }
+
+/* ====================================== */
+/* Returns 1 if s represents an integer   */
+/* else 0.                                */
+/* s != NULL is assumed.                  */
+/* 0 and 0x prefixes are not understood.  */
+/* ====================================== */
+int
+is_integer(const char * const s)
+{
+  char * end;
+
+  strtol(s, &end, 10);
+  return (*end == '\0');
+}
diff --git a/utils.h b/utils.h
index 17e52dd..8c69b8e 100644
--- a/utils.h
+++ b/utils.h
@@ -62,4 +62,7 @@ isprint8(int i);
 int
 xwcscasecmp(const wchar_t * w1s, const wchar_t * w2s);
 
+int
+is_integer(const char * const s);
+
 #endif