diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0a7b017b..28232d96 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -361,6 +361,15 @@ target_link_modules(toxencryptsave toxcore)
 
 find_program(SPECTEST NAMES tox-spectest)
 
+if(NOT SPECTEST)
+  find_program(STACK NAMES stack)
+  if(STACK)
+    set(SPECTEST
+      ${STACK} --stack-yaml ${toxcore_SOURCE_DIR}/../stack.yaml exec --
+      tox-spectest)
+  endif()
+endif()
+
 if(SPECTEST AND MSGPACK_FOUND)
   add_c_executable(toxcore-sut
     testing/hstox/binary_decode.c
diff --git a/other/travis/hstox-install b/other/travis/hstox-install
index fccae0be..773bf388 100755
--- a/other/travis/hstox-install
+++ b/other/travis/hstox-install
@@ -12,8 +12,11 @@ cabal install happy
 git clone --recursive --depth=1 https://github.com/TokTok/hs-toxcore ../hs-toxcore
 git clone --depth=1 https://github.com/msgpack/msgpack-c testing/hstox/msgpack-c
 
-# Install the hstox test runner.
-(cd ../hs-toxcore && cabal install --disable-library-profiling)
-
-# Install toxcore dependencies.
+# Install toxcore dependencies before hstox, as hstox needs libsodium.
 . other/travis/toxcore-linux-install
+
+# Install the hstox test runner.
+CABAL_FLAGS="--disable-library-profiling"
+CABAL_FLAGS="$CABAL_FLAGS --extra-include-dirs=$CACHE_DIR/include"
+CABAL_FLAGS="$CABAL_FLAGS --extra-lib-dirs=$CACHE_DIR/lib"
+(cd ../hs-toxcore && cabal install $CABAL_FLAGS)
diff --git a/testing/hstox/binary_decode.c b/testing/hstox/binary_decode.c
index fb3bca43..588b9a7c 100644
--- a/testing/hstox/binary_decode.c
+++ b/testing/hstox/binary_decode.c
@@ -1,3 +1,4 @@
+#define _BSD_SOURCE
 #include "methods.h"
 
 #include "byteswap.h"
@@ -9,19 +10,17 @@
 static void decode_bytestring(msgpack_object_bin args, msgpack_packer *res,
                               int64_t min_length)
 {
-    int64_t length;
-    uint64_t tmp;
-
     SUCCESS {
         if (args.size < sizeof(uint64_t))
         {
             // Not enough space to even fit the size.
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
             return;
         }
 
+        uint64_t tmp;
         memcpy(&tmp, args.ptr, sizeof(uint64_t));
-        length = be64toh(tmp);
+        int64_t length = be64toh(tmp);
 
         // TODO(iphydf): Get rid of this case if/when
         // https://github.com/kolmodin/binary/issues/127 is fixed. This is a
@@ -37,14 +36,17 @@ static void decode_bytestring(msgpack_object_bin args, msgpack_packer *res,
         {
             if (length < min_length) {
                 // CipherTexts need at least a MAC.
-                msgpack_pack_nil(res);
+                msgpack_pack_uint8(res, 0);
                 return;
             }
 
+            msgpack_pack_array(res, 2);
+            msgpack_pack_uint8(res, 1);
+
             msgpack_pack_bin(res, args.size - sizeof(uint64_t));
             msgpack_pack_bin_body(res, args.ptr + sizeof(uint64_t), args.size - sizeof(uint64_t));
         } else {
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         }
     }
 }
@@ -61,6 +63,11 @@ METHOD(bin, Binary_decode, DhtPacket)
     return pending;
 }
 
+METHOD(bin, Binary_decode, DhtRequestPacket)
+{
+    return pending;
+}
+
 METHOD(bin, Binary_decode, HostAddress)
 {
     return pending;
@@ -81,8 +88,11 @@ METHOD(bin, Binary_decode, KeyPair)
     SUCCESS {
         if (args.size != 64)
         {
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         } else {
+            msgpack_pack_array(res, 2);
+            msgpack_pack_uint8(res, 1);
+
             msgpack_pack_array(res, 2);
             msgpack_pack_bin(res, 32);
             msgpack_pack_bin_body(res, args.ptr, 32);
@@ -113,6 +123,9 @@ METHOD(bin, Binary_decode, NodeInfo)
     SUCCESS {
         if (len > 0 && data_processed > 0 && data_processed == args.size)
         {
+            msgpack_pack_array(res, 2);
+            msgpack_pack_uint8(res, 1);
+
             msgpack_pack_array(res, 3);
             msgpack_pack_uint8(res, tcp);
             msgpack_pack_array(res, 2);
@@ -133,7 +146,7 @@ METHOD(bin, Binary_decode, NodeInfo)
             msgpack_pack_bin(res, CRYPTO_PUBLIC_KEY_SIZE);
             msgpack_pack_bin_body(res, &node.public_key, CRYPTO_PUBLIC_KEY_SIZE);
         } else {
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         }
     }
 
@@ -160,7 +173,7 @@ METHOD(bin, Binary_decode, PacketKind)
     SUCCESS {
         if (args.size != 1)
         {
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         } else {
             uint8_t kind = args.ptr[0];
             size_t  i;
@@ -168,13 +181,15 @@ METHOD(bin, Binary_decode, PacketKind)
             for (i = 0; i < sizeof packet_kinds / sizeof *packet_kinds; i++)
             {
                 if (packet_kinds[i] == kind) {
+                    msgpack_pack_array(res, 2);
+                    msgpack_pack_uint8(res, 1);
                     msgpack_pack_fix_uint8(res, i);
                     return 0;
                 }
             }
 
             // Packet kind not found => error.
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         }
     }
     return 0;
@@ -199,9 +214,11 @@ METHOD(bin, Binary_decode, PortNumber)
             uint16_t tmp;
             memcpy(&tmp, args.ptr, 2);
             uint16_t port = ntohs(tmp);
+            msgpack_pack_array(res, 2);
+            msgpack_pack_uint8(res, 1);
             msgpack_pack_uint16(res, port);
         } else {
-            msgpack_pack_nil(res);
+            msgpack_pack_uint8(res, 0);
         }
     }
 
@@ -235,6 +252,7 @@ METHOD(array, Binary, decode)
         return Binary_decode_##TYPE(args.ptr[1].via.bin, res)
     DISPATCH(CipherText);
     DISPATCH(DhtPacket);
+    DISPATCH(DhtRequestPacket);
     DISPATCH(HostAddress);
     DISPATCH(Word64);
     DISPATCH(Key_PublicKey);
diff --git a/testing/hstox/binary_encode.c b/testing/hstox/binary_encode.c
index 8809be28..aad94f5f 100644
--- a/testing/hstox/binary_encode.c
+++ b/testing/hstox/binary_encode.c
@@ -1,3 +1,4 @@
+#define _BSD_SOURCE
 #include "methods.h"
 
 #include "byteswap.h"
@@ -22,6 +23,11 @@ METHOD(array, Binary_encode, DhtPacket)
     return pending;
 }
 
+METHOD(array, Binary_encode, DhtRequestPacket)
+{
+    return pending;
+}
+
 METHOD(array, Binary_encode, HostAddress)
 {
     return pending;
@@ -231,6 +237,7 @@ METHOD(array, Binary, encode)
   } while (0)
     DISPATCH(CipherText, BIN, bin);
     DISPATCH(DhtPacket, ARRAY, array);
+    DISPATCH(DhtRequestPacket, ARRAY, array);
     DISPATCH(HostAddress, ARRAY, array);
     DISPATCH(Word64, POSITIVE_INTEGER, u64);
     DISPATCH(Key_PublicKey, BIN, bin);
diff --git a/testing/hstox/driver.c b/testing/hstox/driver.c
index 7a9a907e..2ae68f1b 100644
--- a/testing/hstox/driver.c
+++ b/testing/hstox/driver.c
@@ -1,3 +1,5 @@
+#define _XOPEN_SOURCE 600
+
 #include <errno.h>
 #include <fcntl.h>
 #include <netdb.h>
@@ -19,7 +21,7 @@
 
 static void __attribute__((__noreturn__)) handle_interrupt(int signum)
 {
-    printf("Caught signal %d; exiting cleanly.\n", signum);
+    fprintf(stderr, "caught signal %d; exiting cleanly.\n", signum);
     exit(0);
 }
 
@@ -92,6 +94,12 @@ static int write_sample_input(msgpack_object req)
 
 static int handle_request(struct settings cfg, int write_fd, msgpack_object req)
 {
+    if (cfg.trace) {
+        fprintf(stderr, "input:  ");
+        msgpack_object_print(stderr, req);
+        fprintf(stderr, "\n");
+    }
+
     msgpack_sbuffer sbuf __attribute__((__cleanup__(msgpack_sbuffer_destroy))); /* buffer */
     msgpack_sbuffer_init(&sbuf); /* initialize buffer */
 
@@ -121,7 +129,7 @@ static int handle_request(struct settings cfg, int write_fd, msgpack_object req)
         if (name.size == (sizeof "rpc.capabilities") - 1 &&
                 memcmp(name.ptr, "rpc.capabilities", name.size) == 0) {
             // 3. Error.
-            msgpack_pack_string(&pk, "Capabilities negiotiation not implemented");
+            msgpack_pack_string(&pk, "capabilities negiotiation not implemented");
             // 4. No result.
             msgpack_pack_nil(&pk);
         } else {
@@ -131,9 +139,9 @@ static int handle_request(struct settings cfg, int write_fd, msgpack_object req)
 
             if (error) {
                 if (cfg.debug) {
-                    printf("Error '%s' in request: ", error);
-                    msgpack_object_print(stdout, req);
-                    printf("\n");
+                    fprintf(stderr, "error '%s' in request: ", error);
+                    msgpack_object_print(stderr, req);
+                    fprintf(stderr, "\n");
                 }
 
                 msgpack_pack_string(&pk, error);
@@ -144,6 +152,15 @@ static int handle_request(struct settings cfg, int write_fd, msgpack_object req)
 
     check_return(E_WRITE, write(write_fd, sbuf.data, sbuf.size));
 
+    if (cfg.trace) {
+        fprintf(stderr, "result: ");
+        msgpack_unpacked res __attribute__((__cleanup__(msgpack_unpacked_destroy)));
+        msgpack_unpacked_init(&res);
+        msgpack_unpack_next(&res, sbuf.data, sbuf.size, NULL);
+        msgpack_object_print(stderr, res.data);
+        fprintf(stderr, "\n");
+    }
+
     return E_OK;
 }
 
@@ -177,7 +194,7 @@ int communicate(struct settings cfg, int read_fd, int write_fd)
                 break;
 
             case MSGPACK_UNPACK_EXTRA_BYTES:
-                printf("EXTRA_BYTES\n");
+                fprintf(stderr, "EXTRA_BYTES\n");
                 break;
 
             case MSGPACK_UNPACK_CONTINUE:
diff --git a/testing/hstox/driver.h b/testing/hstox/driver.h
index 219df8a1..150d5cdd 100644
--- a/testing/hstox/driver.h
+++ b/testing/hstox/driver.h
@@ -7,6 +7,8 @@
 struct settings {
     // Print the msgpack object on test failure.
     bool debug;
+    // Print all inputs and outputs to stderr.
+    bool trace;
     // Write test sample files into test-inputs/. These files, one per test
     // method, are used to seed the fuzzer.
     bool collect_samples;
diff --git a/testing/hstox/fuzz_main.c b/testing/hstox/fuzz_main.c
index ff66a166..6f223eb2 100644
--- a/testing/hstox/fuzz_main.c
+++ b/testing/hstox/fuzz_main.c
@@ -12,7 +12,7 @@
 #endif
 int main(int argc, char **argv)
 {
-    struct settings cfg = {false, false};
+    struct settings cfg = {false, false, false};
 #ifdef __AFL_LOOP
 
     while (__AFL_LOOP(ITERATIONS))
diff --git a/testing/hstox/test_main.c b/testing/hstox/test_main.c
index 7ac18da0..70f0b95c 100644
--- a/testing/hstox/test_main.c
+++ b/testing/hstox/test_main.c
@@ -57,7 +57,7 @@ static char const *error_desc(int code)
 #endif
 int main(void)
 {
-    struct settings cfg    = {true, true};
+    struct settings cfg    = {true, false, true};
     uint32_t        result = network_main(cfg, PORT, TIMEOUT);
     int             line   = result >> 16;
     int             error  = (result >> 8) & 0xff;
diff --git a/testing/hstox/util.h b/testing/hstox/util.h
index c00578a2..c4095994 100644
--- a/testing/hstox/util.h
+++ b/testing/hstox/util.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdarg.h>
+
 #include <msgpack.h>
 
 #define check_return(err, expr)                                                                    \