diff --git a/README.md b/README.md
index 8de7664..64e079e 100644
--- a/README.md
+++ b/README.md
@@ -651,6 +651,8 @@ to the expected behavior.
 * Fix for [#203](https://github.com/gulrak/filesystem/issues/203), directory
   iteration and `proximate()` are available in builds without exception
   support, with iteration errors terminating the process.
+* Fix for [#191](https://github.com/gulrak/filesystem/issues/191), appending
+  to a host-only UNC path now inserts the missing separator.
 * Fix for [#185](https://github.com/gulrak/filesystem/issues/185),
   `lexically_normal()` now preserves unresolved parent components in relative
   paths.
diff --git a/include/ghc/filesystem.hpp b/include/ghc/filesystem.hpp
index 8f6529f..70e21b7 100644
--- a/include/ghc/filesystem.hpp
+++ b/include/ghc/filesystem.hpp
@@ -2623,10 +2623,16 @@ GHC_INLINE path& path::operator/=(const path& p)
         assign(p);
         return *this;
     }
+    bool isHostOnlyUncPath = false;
+#ifdef GHC_OS_WINDOWS
+    const auto rootNameLength = root_name_length();
+    isHostOnlyUncPath = rootNameLength == _path.length() && rootNameLength > _prefixLength + 2 &&
+        _path[_prefixLength] == preferred_separator && _path[_prefixLength + 1] == preferred_separator;
+#endif
     if (p.has_root_directory()) {
         assign(root_name());
     }
-    else if ((!has_root_directory() && is_absolute()) || has_filename()) {
+    else if ((!has_root_directory() && is_absolute()) || has_filename() || isHostOnlyUncPath) {
         _path += preferred_separator;
     }
     auto iter = p.begin();
diff --git a/test/filesystem_test.cpp b/test/filesystem_test.cpp
index fc202fa..9502882 100644
--- a/test/filesystem_test.cpp
+++ b/test/filesystem_test.cpp
@@ -490,6 +490,14 @@ TEST_CASE("fs.path.append - path appends", "[filesystem][path][fs.path.append]")
     CHECK(fs::path("c:") / "" == "c:");
     CHECK(fs::path("c:foo") / "/bar" == "c:/bar");
     CHECK(fs::path("c:foo") / "c:bar" == "c:foo/bar");
+    CHECK(fs::path(R"(\\server)") / "abc" == R"(\\server\abc)");
+    CHECK(fs::path(R"(\\server)") / "" == R"(\\server\)");
+    CHECK(fs::path(R"(\\server\)") / "abc" == R"(\\server\abc)");
+    CHECK(fs::path(R"(\\server\share)") / "abc" == R"(\\server\share\abc)");
+    CHECK(fs::path(R"(\\server)") / R"(\abc)" == R"(\\server\abc)");
+    CHECK(fs::path("c:") / "abc" == "c:abc");
+    CHECK(fs::path(R"(c:\)") / "abc" == R"(c:\abc)");
+    CHECK(fs::path(R"(\rooted)") / "abc" == R"(\rooted\abc)");
 #else
     CHECK(fs::path("foo") / "" == "foo/");
     CHECK(fs::path("foo") / "/bar" == "/bar");