diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index f30fedf2948..36fcab95d7b 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,13 @@
+2019-01-30  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/89117
+	* src/c++17/fs_path.cc (path::replace_extension): Erase extension from
+	final component as well as from _M_pathname. Append the dot using
+	operator+= instead of only to _M_pathname.
+	(path::_M_find_extension): Reformat slightly.
+	* testsuite/27_io/filesystem/path/modifiers/replace_extension.cc:
+	Add more test cases.
+
 2019-01-30  Ulrich Drepper  <drepper@redhat.com>
 
 	* doc/xml/manual/status_cxx2020.xml: Update P0600 entry.
diff --git a/libstdc++-v3/src/c++17/fs_path.cc b/libstdc++-v3/src/c++17/fs_path.cc
index 34de52f3a0f..db6a1cb29d8 100644
--- a/libstdc++-v3/src/c++17/fs_path.cc
+++ b/libstdc++-v3/src/c++17/fs_path.cc
@@ -1258,17 +1258,16 @@ path::replace_extension(const path& replacement)
 	_M_pathname.erase(ext.second);
       else
 	{
-	  const auto& back = _M_cmpts.back();
-	  if (ext.first != &back._M_pathname)
-	    _GLIBCXX_THROW_OR_ABORT(
-		std::logic_error("path::replace_extension failed"));
+	  auto& back = _M_cmpts.back();
+	  __glibcxx_assert( ext.first == &back._M_pathname );
+	  back._M_pathname.erase(ext.second);
 	  _M_pathname.erase(back._M_pos + ext.second);
 	}
     }
    // If replacement is not empty and does not begin with a dot character,
    // a dot character is appended
   if (!replacement.empty() && replacement.native()[0] != dot)
-    _M_pathname += dot;
+    operator+=(".");
   operator+=(replacement);
   return *this;
 }
@@ -1803,8 +1802,9 @@ path::_M_find_extension() const
 	{
 	  if (sz <= 2 && (*s)[0] == dot)
 	    return { s, string_type::npos };
-	  const auto pos = s->rfind(dot);
-	  return { s, pos ? pos : string_type::npos };
+	  if (const auto pos = s->rfind(dot))
+	    return { s , pos };
+	  return { s, string_type::npos };
 	}
     }
   return {};
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/modifiers/replace_extension.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/modifiers/replace_extension.cc
index df4b77aa116..98f2e6e4c41 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/modifiers/replace_extension.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/modifiers/replace_extension.cc
@@ -33,6 +33,15 @@ test01()
   compare_paths( path("/foo.txt").replace_extension("cpp"), "/foo.cpp" );
   compare_paths( path("/foo.txt").replace_extension(".cpp"), "/foo.cpp" );
   compare_paths( path("/").replace_extension("bar"), "/.bar" );
+  compare_paths( path("/").replace_extension(".bar"), "/.bar" );
+  compare_paths( path("/dir/").replace_extension("bar"), "/dir/.bar" );
+  compare_paths( path("dir/foo").replace_extension("bar"), "dir/foo.bar" );
+
+  // PR 89117:
+  compare_paths( path("/foo.txt").replace_extension(), "/foo" );
+  compare_paths( path("foo.txt").replace_extension(), "foo" );
+  compare_paths( path("/foo").replace_extension(), "/foo" );
+  compare_paths( path("foo").replace_extension(), "foo" );
 }
 
 void