diff --git a/ext/strscan/strscan.c b/ext/strscan/strscan.c
index da02291478..1894ed7fb3 100644
--- a/ext/strscan/strscan.c
+++ b/ext/strscan/strscan.c
@@ -1862,8 +1862,13 @@ strscan_integer_at(int argc, VALUE *argv, VALUE self)
         return Qnil;
 
     beg = adjust_register_position(p, p->regs.beg[i]);
+    if (beg > S_LEN(p))
+        return Qnil;
     end = adjust_register_position(p, p->regs.end[i]);
+    end = minl(end, S_LEN(p));
     len = end - beg;
+    if (len == 0)
+        return Qnil;
     ptr = S_PBEG(p) + beg;
 #ifdef HAVE_RB_INT_PARSE_CSTR
     {
diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 96a1badb1f..966d62b226 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -578,6 +578,26 @@ module StringScannerTests
     assert_integer_at(s, 0, 0) # 0xaf
   end
 
+  def test_integer_at_shrunk
+    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
+
+    s = create_string_scanner(+"before 29 after")
+    s.skip_until(" ")
+    assert_equal("29", s.scan(/\d+/))
+    s.string.replace("before ")
+    assert_nil(s.integer_at(0))
+  end
+
+  def test_integer_at_shrunk_partial
+    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
+
+    s = create_string_scanner(+"before 29 after")
+    s.skip_until(" ")
+    assert_equal("29", s.scan(/\d+/))
+    s.string.replace("before 2")
+    assert_integer_at(s, 2)
+  end
+
   def test_pre_match
     s = create_string_scanner('a b c d e')
     s.scan(/\w/)