diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d8f9325..4b51e425 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@ Version 260:
 
 * More split compilation in rfc7230.hpp
 * Qualify calls to `beast::iequals` in basic_parser.ipp
+* More split compilation in websocket/detail/mask.hpp
 
 --------------------------------------------------------------------------------
 
diff --git a/include/boost/beast/src.hpp b/include/boost/beast/src.hpp
index 6debe246..2376c3fc 100644
--- a/include/boost/beast/src.hpp
+++ b/include/boost/beast/src.hpp
@@ -52,6 +52,7 @@ the program, with the macro BOOST_BEAST_SEPARATE_COMPILATION defined.
 #include <boost/beast/http/impl/verb.ipp>
 
 #include <boost/beast/websocket/detail/hybi13.ipp>
+#include <boost/beast/websocket/detail/mask.ipp>
 #include <boost/beast/websocket/detail/pmd_extension.ipp>
 #include <boost/beast/websocket/detail/prng.ipp>
 #include <boost/beast/websocket/detail/service.ipp>
diff --git a/include/boost/beast/websocket/detail/mask.hpp b/include/boost/beast/websocket/detail/mask.hpp
index ade89fda..58797372 100644
--- a/include/boost/beast/websocket/detail/mask.hpp
+++ b/include/boost/beast/websocket/detail/mask.hpp
@@ -26,62 +26,27 @@ namespace detail {
 
 using prepared_key = std::array<unsigned char, 4>;
 
-inline
+BOOST_BEAST_DECL
 void
-prepare_key(prepared_key& prepared, std::uint32_t key)
-{
-    prepared[0] = (key >>  0) & 0xff;
-    prepared[1] = (key >>  8) & 0xff;
-    prepared[2] = (key >> 16) & 0xff;
-    prepared[3] = (key >> 24) & 0xff;
-}
-
-template<std::size_t N>
-void
-rol(std::array<unsigned char, N>& v, std::size_t n)
-{
-    auto v0 = v;
-    for(std::size_t i = 0; i < v.size(); ++i )
-        v[i] = v0[(i + n) % v.size()];
-}
+prepare_key(prepared_key& prepared, std::uint32_t key);
 
 // Apply mask in place
 //
-inline
+BOOST_BEAST_DECL
 void
-mask_inplace(net::mutable_buffer& b, prepared_key& key)
-{
-    auto n = b.size();
-    auto mask = key; // avoid aliasing
-    auto p = static_cast<unsigned char*>(b.data());
-    while(n >= 4)
-    {
-        for(int i = 0; i < 4; ++i)
-            p[i] ^= mask[i];
-        p += 4;
-        n -= 4;
-    }
-    if(n > 0)
-    {
-        for(std::size_t i = 0; i < n; ++i)
-            p[i] ^= mask[i];
-        rol(key, n);
-    }
-}
+mask_inplace(net::mutable_buffer const& b, prepared_key& key);
 
 // Apply mask in place
 //
-template<
-    class MutableBufferSequence,
-    class KeyType>
+template<class MutableBufferSequence>
 void
 mask_inplace(
     MutableBufferSequence const& buffers,
-    KeyType& key)
+    prepared_key& key)
 {
     for(net::mutable_buffer b :
             beast::buffers_range_ref(buffers))
-        mask_inplace(b, key);
+        detail::mask_inplace(b, key);
 }
 
 } // detail
@@ -89,4 +54,10 @@ mask_inplace(
 } // beast
 } // boost
 
+
+#if BOOST_BEAST_HEADER_ONLY
+#include <boost/beast/websocket/detail/mask.ipp>
+#endif
+
+
 #endif
diff --git a/include/boost/beast/websocket/detail/mask.ipp b/include/boost/beast/websocket/detail/mask.ipp
new file mode 100644
index 00000000..6c36d56b
--- /dev/null
+++ b/include/boost/beast/websocket/detail/mask.ipp
@@ -0,0 +1,66 @@
+//
+// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_WEBSOCKET_DETAIL_MASK_IPP
+#define BOOST_BEAST_WEBSOCKET_DETAIL_MASK_IPP
+
+#include <boost/beast/websocket/detail/mask.hpp>
+
+namespace boost {
+namespace beast {
+namespace websocket {
+namespace detail {
+
+void
+prepare_key(prepared_key& prepared, std::uint32_t key)
+{
+    prepared[0] = (key >>  0) & 0xff;
+    prepared[1] = (key >>  8) & 0xff;
+    prepared[2] = (key >> 16) & 0xff;
+    prepared[3] = (key >> 24) & 0xff;
+}
+
+inline
+void
+rol(prepared_key& v, std::size_t n)
+{
+    auto v0 = v;
+    for(std::size_t i = 0; i < v.size(); ++i )
+        v[i] = v0[(i + n) % v.size()];
+}
+
+// Apply mask in place
+//
+void
+mask_inplace(net::mutable_buffer const& b, prepared_key& key)
+{
+    auto n = b.size();
+    auto const mask = key; // avoid aliasing
+    auto p = static_cast<unsigned char*>(b.data());
+    while(n >= 4)
+    {
+        for(int i = 0; i < 4; ++i)
+            p[i] ^= mask[i];
+        p += 4;
+        n -= 4;
+    }
+    if(n > 0)
+    {
+        for(std::size_t i = 0; i < n; ++i)
+            p[i] ^= mask[i];
+        rol(key, n);
+    }
+}
+
+} // detail
+} // websocket
+} // beast
+} // boost
+
+#endif