diff --git a/include/boost/fixed_string/impl/fixed_string.hpp b/include/boost/fixed_string/impl/fixed_string.hpp
index d5d3bfb..dd2a17f 100644
--- a/include/boost/fixed_string/impl/fixed_string.hpp
+++ b/include/boost/fixed_string/impl/fixed_string.hpp
@@ -320,7 +320,7 @@ insert(
         BOOST_FIXED_STRING_THROW(std::length_error{
             "size() + count > max_size()"});
     const bool inside = s <= &s_[size()] && s >= &s_[0];
-    if (!inside || (inside && (&s[count - 1] < &s_[index])))
+    if (!inside || (inside && ((s - s_) + count <= index)))
     {
       Traits::move(&s_[index + count], &s_[index], size() - index + 1);
       Traits::copy(&s_[index], s, count);
@@ -597,7 +597,7 @@ replace(
   const bool inside = s <= &s_[size()] && s >= &s_[0];
   if (inside && (s - &s_[0]) == pos && n1 == n2)
     return *this;
-  if (!inside || (inside && (&s[n2 - 1] < &s_[pos])))
+  if (!inside || (inside && ((s - s_) + n2 <= pos)))
   {
     // source outside
     Traits::move(&s_[pos + n2], &s_[pos + n1], size() - pos - n1 + 1);
diff --git a/test/fixed_string.cpp b/test/fixed_string.cpp
index 65cfd2f..b0d05c3 100644
--- a/test/fixed_string.cpp
+++ b/test/fixed_string.cpp
@@ -23,7 +23,7 @@ testS(const S& s, typename S::size_type pos, typename S::size_type n)
   if (pos <= s.size())
   {
     typename S::string_view_type str = s.substr(pos, n);
-    typename S::size_type rlen = std::min(n, s.size() - pos);
+    typename S::size_type rlen = (std::min)(n, s.size() - pos);
     return (S::traits_type::compare(s.data() + pos, str.data(), rlen) == 0);
   }
   else
@@ -319,6 +319,10 @@ testAssignment()
     BOOST_TEST(fixed_string<3>{}.assign(fixed_string<5>{"abc"}) == "abc");
     BOOST_TEST(fixed_string<3>{"*"}.assign(fixed_string<5>{"abc"}) == "abc");
     BOOST_TEST(fixed_string<3>{"***"}.assign(fixed_string<5>{"abc"}) == "abc");
+    {
+      fixed_string<3> s("***");
+      BOOST_TEST(s.assign(s) == s);
+    }
     BOOST_TEST_THROWS(fixed_string<3>{}.assign(fixed_string<5>{"abcde"}), std::length_error);
 
     // assign(fixed_string<M, CharT, Traits> const& s, size_type pos, size_type count = npos)
@@ -5685,6 +5689,10 @@ testReplace()
     fixed_string<20> fs2 = "0123456789";
     BOOST_TEST(fs2.replace(0, 10, fs2.data(), 5) == "01234");
   }
+  {
+    fixed_string<20> fs1 = "helloworld";
+    BOOST_TEST(fs1.replace(4, 3, fs1.data() + 1, 3) == "hellellrld");
+  }
 
   // replace(size_type pos1, size_type n1, const basic_string& str);
   {