diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -145,6 +145,7 @@
 	utilmoneystr.cpp
 	utilstrencodings.cpp
 	utiltime.cpp
+	util/bytevectorhash.cpp
 )
 
 target_compile_definitions(util PUBLIC HAVE_CONFIG_H)
diff --git a/src/Makefile.am b/src/Makefile.am
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -204,6 +204,7 @@
   util.h \
   utilmoneystr.h \
   utiltime.h \
+  util/bytevectorhash.h \
   validation.h \
   validationinterface.h \
   versionbits.h \
@@ -452,6 +453,7 @@
   utilmoneystr.cpp \
   utilstrencodings.cpp \
   utiltime.cpp \
+  util/bytevectorhash.cpp \
   $(BITCOIN_CORE_H)
 
 if GLIBC_BACK_COMPAT
diff --git a/src/blockfilter.h b/src/blockfilter.h
--- a/src/blockfilter.h
+++ b/src/blockfilter.h
@@ -9,9 +9,10 @@
 #include <serialize.h>
 #include <uint256.h>
 #include <undo.h>
+#include <util/bytevectorhash.h>
 
 #include <cstdint>
-#include <set>
+#include <unordered_set>
 #include <vector>
 
 /**
@@ -20,8 +21,8 @@
  */
 class GCSFilter {
 public:
-    typedef std::vector<uint8_t> Element;
-    typedef std::set<Element> ElementSet;
+    typedef std::vector<unsigned char> Element;
+    typedef std::unordered_set<Element, ByteVectorHash> ElementSet;
 
     struct Params {
         uint64_t m_siphash_k0;
diff --git a/src/util/bytevectorhash.h b/src/util/bytevectorhash.h
new file mode 100644
--- /dev/null
+++ b/src/util/bytevectorhash.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_BYTEVECTORHASH_H
+#define BITCOIN_UTIL_BYTEVECTORHASH_H
+
+#include <stdint.h>
+#include <vector>
+
+/**
+ * Implementation of Hash named requirement for types that internally store a
+ * byte array. This may be used as the hash function in std::unordered_set or
+ * std::unordered_map over such types. Internally, this uses a random instance
+ * of SipHash-2-4.
+ */
+class ByteVectorHash final {
+private:
+    uint64_t m_k0, m_k1;
+
+public:
+    ByteVectorHash();
+    size_t operator()(const std::vector<unsigned char> &input) const;
+};
+
+#endif // BITCOIN_UTIL_BYTEVECTORHASH_H
diff --git a/src/util/bytevectorhash.cpp b/src/util/bytevectorhash.cpp
new file mode 100644
--- /dev/null
+++ b/src/util/bytevectorhash.cpp
@@ -0,0 +1,17 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <crypto/siphash.h>
+#include <random.h>
+#include <util/bytevectorhash.h>
+
+ByteVectorHash::ByteVectorHash() {
+    GetRandBytes(reinterpret_cast<unsigned char *>(&m_k0), sizeof(m_k0));
+    GetRandBytes(reinterpret_cast<unsigned char *>(&m_k1), sizeof(m_k1));
+}
+
+size_t ByteVectorHash::
+operator()(const std::vector<unsigned char> &input) const {
+    return CSipHasher(m_k0, m_k1).Write(input.data(), input.size()).Finalize();
+}