diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index fe985de..dcfe888 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -4731,6 +4731,46 @@
   delete('XdebugFunc')
 enddef
 
+func Test_debug_running_out_of_lines()
+  CheckRunVimInTerminal
+
+  " call indirectly to avoid compilation error for missing functions
+  call Run_Test_debug_running_out_of_lines()
+endfunc
+
+def Run_Test_debug_running_out_of_lines()
+  var lines =<< trim END
+      vim9script
+      def Crash()
+          #
+          #
+          #
+          #
+          #
+          #
+          #
+          if true
+              #
+          endif
+      enddef
+      breakadd func Crash
+      Crash()
+  END
+  writefile(lines, 'XdebugFunc')
+  var buf = RunVimInTerminal('-S XdebugFunc', {rows: 6, wait_for_ruler: 0})
+  WaitForAssert(() => assert_match('^>', term_getline(buf, 6)))
+
+  term_sendkeys(buf, "next\<CR>")
+  TermWait(buf)
+  WaitForAssert(() => assert_match('^>', term_getline(buf, 6)))
+
+  term_sendkeys(buf, "cont\<CR>")
+  TermWait(buf)
+
+  StopVimInTerminal(buf)
+  delete('XdebugFunc')
+enddef
+
 def ProfiledWithLambda()
   var n = 3
   echo [[1, 2], [3, 4]]->filter((_, l) => l[0] == n)
diff --git a/src/version.c b/src/version.c
index e310f76..e9d77a9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3878,
+/**/
     3877,
 /**/
     3876,
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 7485112..72cbb90 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -1660,7 +1660,8 @@
     if (end_lnum > iptr->isn_lnum)
     {
 	ga_init2(&ga, sizeof(char_u *), 10);
-	for (lnum = iptr->isn_lnum; lnum < end_lnum; ++lnum)
+	for (lnum = iptr->isn_lnum; lnum < end_lnum
+				     && lnum <= ufunc->uf_lines.ga_len; ++lnum)
 	{
 	    char_u *p = ((char_u **)ufunc->uf_lines.ga_data)[lnum - 1];