diff --git a/sdk/core/azure-core/src/http/winhttp/win_http_transport.cpp b/sdk/core/azure-core/src/http/winhttp/win_http_transport.cpp
index c480b67b2..a50f7aff6 100644
--- a/sdk/core/azure-core/src/http/winhttp/win_http_transport.cpp
+++ b/sdk/core/azure-core/src/http/winhttp/win_http_transport.cpp
@@ -35,9 +35,12 @@ inline std::wstring HttpMethodToWideString(HttpMethod method)
 // This assumes the input string is always null-terminated.
 std::wstring StringToWideString(const std::string& str)
 {
+  // Since the strings being converted to wstring can be provided by the end user, and can contain
+  // invalid characters, use the MB_ERR_INVALID_CHARS to validate and fail.
+
   // Passing in -1 so that the function processes the entire input string, including the terminating
   // null character.
-  int sizeNeeded = MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, 0, 0);
+  int sizeNeeded = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS, str.c_str(), -1, 0, 0);
   if (sizeNeeded == 0)
   {
     // Errors include:
@@ -52,7 +55,8 @@ std::wstring StringToWideString(const std::string& str)
   }
 
   std::wstring wideStr(sizeNeeded, L'\0');
-  if (MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, &wideStr[0], sizeNeeded) == 0)
+  if (MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS, str.c_str(), -1, &wideStr[0], sizeNeeded)
+      == 0)
   {
     DWORD error = GetLastError();
     throw Azure::Core::Http::TransportException(
@@ -74,6 +78,11 @@ std::string WideStringToString(const std::wstring& wideString)
         "Input wide string is too large to fit within a 32-bit int.");
   }
 
+  // Note, we are not using the flag WC_ERR_INVALID_CHARS here, because it is assumed the service
+  // returns correctly encoded response headers and reason phrase strings.
+  // The transport layer shouldn't do additional validation, and if WideCharToMultiByte replaces
+  // invalid characters with the replacement character, that is fine.
+
   int wideStrLength = static_cast<int>(wideStrSize);
   int sizeNeeded
       = WideCharToMultiByte(CP_UTF8, 0, wideString.c_str(), wideStrLength, NULL, 0, NULL, NULL);
diff --git a/sdk/core/azure-core/test/ut/transport_adapter_base.cpp b/sdk/core/azure-core/test/ut/transport_adapter_base.cpp
index 184c97498..9071e25aa 100644
--- a/sdk/core/azure-core/test/ut/transport_adapter_base.cpp
+++ b/sdk/core/azure-core/test/ut/transport_adapter_base.cpp
@@ -408,6 +408,70 @@ namespace Azure { namespace Core { namespace Test {
         Azure::Core::RequestFailedException);
   }
 
+  TEST_P(TransportAdapter, validNonAsciiHost)
+  {
+    {
+      Azure::Core::Url host(u8"http://unresolvedHost\u6F22\u5B57.org/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+    {
+      Azure::Core::Url host("http://unresolvedHost\xE9\x87\x91.org/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+    {
+      Azure::Core::Url host(u8"http://unresolvedHost\uC328.org/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+    {
+      Azure::Core::Url host("http://\0/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+  }
+
+  TEST_P(TransportAdapter, invalidNonAsciiHost)
+  {
+    {
+      Azure::Core::Url host("http://unresolvedHost\xC0\x41\x42\xFE\xFE\xFF\xFF.org/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+    {
+      Azure::Core::Url host("http://\xC0\x76\x77/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+    {
+      Azure::Core::Url host("http://\xD8\x00\x01\x00/get");
+
+      auto request = Azure::Core::Http::Request(Azure::Core::Http::HttpMethod::Get, host);
+      EXPECT_THROW(
+          m_pipeline->Send(request, Azure::Core::Context::ApplicationContext),
+          Azure::Core::Http::TransportException);
+    }
+  }
+
   TEST_P(TransportAdapter, dynamicCast)
   {
     Azure::Core::Url host("http://unresolvedHost.org/get");