diff --git a/Release/include/cpprest/asyncrt_utils.h b/Release/include/cpprest/asyncrt_utils.h
index a38702f412..4166eb8c48 100644
--- a/Release/include/cpprest/asyncrt_utils.h
+++ b/Release/include/cpprest/asyncrt_utils.h
@@ -373,6 +373,26 @@ inline bool __cdecl is_alnum(Elem ch) CPPREST_NOEXCEPT
     return (uch <= static_cast<UElem>('z') && is_alnum(static_cast<unsigned char>(uch)));
 }
 
+/// <summary>
+/// Our own implementation of whitespace test instead of std::isspace to avoid
+/// taking global lock for performance reasons.
+/// The following characters are considered whitespace:
+/// 0x09 == Horizontal Tab
+/// 0x0A == Line Feed
+/// 0x0B == Vertical Tab
+/// 0x0C == Form Feed
+/// 0x0D == Carrage Return
+/// 0x20 == Space
+/// </summary>
+template<class Elem>
+inline bool __cdecl is_space(Elem ch) CPPREST_NOEXCEPT
+{
+    // assumes 'x' == L'x' for the ASCII range
+    typedef typename std::make_unsigned<Elem>::type UElem;
+    const auto uch = static_cast<UElem>(ch);
+    return uch == 0x20u || (uch >= 0x09u && uch <= 0x0Du);
+}
+
 /// <summary>
 /// Simplistic implementation of make_unique. A better implementation would be based on variadic templates
 /// and therefore not be compatible with Dev10.
diff --git a/Release/src/http/client/http_client_winhttp.cpp b/Release/src/http/client/http_client_winhttp.cpp
index 249bfcd52c..f4b97f509a 100644
--- a/Release/src/http/client/http_client_winhttp.cpp
+++ b/Release/src/http/client/http_client_winhttp.cpp
@@ -15,6 +15,7 @@
 #include "stdafx.h"
 
 #include "../common/x509_cert_utilities.h"
+#include "../common/internal_http_helpers.h"
 #include "cpprest/http_headers.h"
 #include "http_client_impl.h"
 #include <Wincrypt.h>
@@ -99,51 +100,6 @@ static http::status_code parse_status_code(HINTERNET request_handle)
     return (unsigned short)_wtoi(buffer.c_str());
 }
 
-// Helper function to trim leading and trailing null characters from a string.
-static void trim_nulls(utility::string_t& str)
-{
-    if (str.empty())
-    {
-        return;
-    }
-
-    auto first = str.begin();
-    auto last = str.end();
-
-    if (*first)
-    {
-        --last;
-        if (*last)
-        {
-            // no nulls to remove
-            return;
-        }
-
-        // nulls at the back to remove
-        do
-        {
-            --last;
-        } while (*last == utility::char_t {});
-        ++last;
-        str.erase(last, str.end());
-        return;
-    }
-
-    // nulls at the front, and maybe the back, to remove
-    first = std::find_if(str.begin(), last, [](const utility::char_t c) { return c != utility::char_t {}; });
-
-    if (first != last)
-    {
-        do
-        {
-            --last;
-        } while (*last == utility::char_t {});
-        ++last;
-    }
-
-    str.assign(first, last);
-}
-
 // Helper function to get the reason phrase from a WinHTTP response.
 static utility::string_t parse_reason_phrase(HINTERNET request_handle)
 {
@@ -159,7 +115,7 @@ static utility::string_t parse_reason_phrase(HINTERNET request_handle)
                         &length,
                         WINHTTP_NO_HEADER_INDEX);
     // WinHTTP reports back the wrong length, trim any null characters.
-    trim_nulls(phrase);
+    ::web::http::details::trim_nulls(phrase);
     return phrase;
 }
 
diff --git a/Release/src/http/common/internal_http_helpers.h b/Release/src/http/common/internal_http_helpers.h
index 2270f7b955..1fbdfdfa58 100644
--- a/Release/src/http/common/internal_http_helpers.h
+++ b/Release/src/http/common/internal_http_helpers.h
@@ -5,6 +5,7 @@
 
 #pragma once
 
+#include "cpprest/asyncrt_utils.h"
 #include "cpprest/details/basic_types.h"
 #include <string>
 
@@ -19,19 +20,71 @@ namespace details
 /// </summary>
 utility::string_t get_default_reason_phrase(status_code code);
 
-// simple helper functions to trim whitespace.
+template<class Char, class Fn>
+void trim_if(std::basic_string<Char>& str, Fn test)
+{
+    if (str.empty())
+    {
+        return;
+    }
+
+    auto first = str.begin();
+    auto last = str.end();
+
+    if (test(*first))
+    {
+        // removals at the front, and maybe the back
+        for (;;)
+        {
+            ++first;
+            if (first == last)
+            {
+                // all removals
+                str.clear();
+                return;
+            }
+
+            if (!test(*first))
+            {
+                break;
+            }
+        }
+
+        do
+        {
+            --last;
+        } while (test(*last));
+        ++last;
+        str.assign(first, last);
+        return;
+    }
+
+    // no removals at the front, only maybe the back
+    --last;
+    if (!test(*last))
+    {
+        // no removals at all
+        return;
+    }
+
+    do
+    {
+        --last;
+    } while (test(*last));
+    ++last;
+    str.erase(last, str.end());
+}
+
+template<class Char>
+void trim_nulls(std::basic_string<Char>& str)
+{
+    trim_if(str, [](const Char c) { return c == Char {}; });
+}
+
 template<class Char>
 void trim_whitespace(std::basic_string<Char>& str)
 {
-    size_t index;
-    // trim left whitespace
-    for (index = 0; index < str.size() && isspace(str[index]); ++index)
-        ;
-    str.erase(0, index);
-    // trim right whitespace
-    for (index = str.size(); index > 0 && isspace(str[index - 1]); --index)
-        ;
-    str.erase(index);
+    trim_if(str, [](const Char c) { return ::utility::details::is_space(c); });
 }
 
 bool validate_method(const utility::string_t& method);