diff --git a/src/include/taler_pq_lib.h b/src/include/taler_pq_lib.h
index 6199444e1..9159cc0f7 100644
--- a/src/include/taler_pq_lib.h
+++ b/src/include/taler_pq_lib.h
@@ -230,7 +230,9 @@ TALER_PQ_query_param_uint64 (const uint64_t *x);
 
 /**
  * Generate query parameter for a JSON object (stored as a string
- * in the DB).
+ * in the DB).  Note that @a x must really be a JSON object or array,
+ * passing just a value (string, integer) is not supported and will
+ * result in an abort.
  *
  * @param x pointer to the json object to pass
  */
@@ -471,7 +473,7 @@ TALER_PQ_result_spec_uint16 (const char *name,
  */
 struct TALER_PQ_ResultSpec
 TALER_PQ_result_spec_uint32 (const char *name,
-                             uint16_t *u32);
+                             uint32_t *u32);
 
 
 /**
diff --git a/src/pq/Makefile.am b/src/pq/Makefile.am
index 746094ce4..2187d494b 100644
--- a/src/pq/Makefile.am
+++ b/src/pq/Makefile.am
@@ -17,7 +17,7 @@ libtalerpq_la_SOURCES = \
 
 libtalerpq_la_LIBADD = \
   $(top_builddir)/src/util/libtalerutil.la  \
-  -lgnunetutil \
+  -lgnunetutil -ljansson \
   -lpq $(XLIB)
 
 libtalerpq_la_LDFLAGS = \
@@ -36,5 +36,5 @@ test_pq_SOURCES = \
 test_pq_LDADD = \
   libtalerpq.la \
   $(top_builddir)/src/util/libtalerutil.la  \
-  -lgnunetutil \
+  -lgnunetutil -ljansson \
   -lpq $(XLIB)
diff --git a/src/pq/db_pq.c b/src/pq/db_pq.c
index 693da2f35..e1a082e44 100644
--- a/src/pq/db_pq.c
+++ b/src/pq/db_pq.c
@@ -237,6 +237,7 @@ TALER_PQ_exec_prepared (PGconn *db_conn,
           char *str;
 
           str = json_dumps (json, JSON_COMPACT);
+          GNUNET_assert (NULL != str);
           scratch[soff++] = str;
           param_values[off] = (void *) str;
           param_lengths[off] = strlen (str);
diff --git a/src/pq/pq_helper.c b/src/pq/pq_helper.c
index 01441dec3..f4b0c0109 100644
--- a/src/pq/pq_helper.c
+++ b/src/pq/pq_helper.c
@@ -294,7 +294,7 @@ TALER_PQ_result_spec_uint16 (const char *name,
  */
 struct TALER_PQ_ResultSpec
 TALER_PQ_result_spec_uint32 (const char *name,
-                             uint16_t *u32)
+                             uint32_t *u32)
 {
   struct TALER_PQ_ResultSpec res =
     {TALER_PQ_RF_UINT32, (void *) u32, sizeof (*u32), (name), NULL };
diff --git a/src/pq/test_pq.c b/src/pq/test_pq.c
index c89313b64..bda227587 100644
--- a/src/pq/test_pq.c
+++ b/src/pq/test_pq.c
@@ -13,7 +13,6 @@
   You should have received a copy of the GNU General Public License along with
   TALER; see the file COPYING.  If not, If not, see <http://www.gnu.org/licenses/>
 */
-
 /**
  * @file pq/test_pq.c
  * @brief Tests for Postgres convenience API
@@ -61,10 +60,14 @@ postgres_prepare (PGconn *db_conn)
            ",namount_frac"
            ",namount_curr"
            ",vsize"
+           ",u16"
+           ",u32"
+           ",u64"
+           ",json"
            ") VALUES "
            "($1, $2, $3, $4, $5, $6,"
-            "$7, $8, $9, $10, $11, $12);",
-           11, NULL);
+            "$7, $8, $9, $10, $11, $12, $13, $14, $15, $16);",
+           16, NULL);
   PREPARE ("test_select",
            "SELECT"
            " pub"
@@ -79,6 +82,10 @@ postgres_prepare (PGconn *db_conn)
            ",namount_frac"
            ",namount_curr"
 	   ",vsize"
+           ",u16"
+           ",u32"
+           ",u64"
+           ",json"
            " FROM test_pq"
            " ORDER BY abs_time DESC "
            " LIMIT 1;",
@@ -116,6 +123,14 @@ run_queries (PGconn *conn)
   char msg[] = "Hello";
   void *msg2;
   size_t msg2_len;
+  uint16_t u16;
+  uint16_t u162;
+  uint32_t u32;
+  uint32_t u322;
+  uint64_t u64;
+  uint64_t u642;
+  json_t *json;
+  json_t *json2;
 
   priv = GNUNET_CRYPTO_rsa_private_key_create (1024);
   pub = GNUNET_CRYPTO_rsa_private_key_get_public (priv);
@@ -130,6 +145,12 @@ run_queries (PGconn *conn)
   GNUNET_assert (GNUNET_OK ==
                  TALER_string_to_amount ("EUR:4.4",
                                          &hamount));
+  u16 = 16;
+  u32 = 32;
+  u64 = 64;
+  json = json_object ();
+  json_object_set (json, "foo", json_integer (42));
+  GNUNET_assert (NULL != json);
   /* FIXME: test TALER_PQ_result_spec_variable_size */
   {
     struct TALER_PQ_QueryParam params_insert[] = {
@@ -141,6 +162,10 @@ run_queries (PGconn *conn)
       TALER_PQ_query_param_amount (&hamount),
       TALER_PQ_query_param_amount_nbo (&namount),
       TALER_PQ_query_param_fixed_size (msg, strlen (msg)),
+      TALER_PQ_query_param_uint16 (&u16),
+      TALER_PQ_query_param_uint32 (&u32),
+      TALER_PQ_query_param_uint64 (&u64),
+      TALER_PQ_query_param_json (json),
       TALER_PQ_query_param_end
     };
     struct TALER_PQ_QueryParam params_select[] = {
@@ -155,6 +180,10 @@ run_queries (PGconn *conn)
       TALER_PQ_result_spec_amount ("hamount", &hamount2),
       TALER_PQ_result_spec_amount_nbo ("namount", &namount2),
       TALER_PQ_result_spec_variable_size ("vsize", &msg2, &msg2_len),
+      TALER_PQ_result_spec_uint16 ("u16", &u162),
+      TALER_PQ_result_spec_uint32 ("u32", &u322),
+      TALER_PQ_result_spec_uint64 ("u64", &u642),
+      TALER_PQ_result_spec_json ("json", &json2),
       TALER_PQ_result_spec_end
     };
 
@@ -219,7 +248,11 @@ run_queries (PGconn *conn)
 		  strncmp (msg,
 			   msg2,
 			   msg2_len));
-
+    GNUNET_break (16 == u162);
+    GNUNET_break (32 == u322);
+    GNUNET_break (64 == u642);
+    GNUNET_break (42 == json_integer_value (json_object_get (json2, "foo")));
+    json_decref (json2);
     TALER_PQ_cleanup_result (results_select);
     PQclear (result);
   }
@@ -269,6 +302,10 @@ main(int argc,
 		   ",namount_frac INT4 NOT NULL"
 		   ",namount_curr VARCHAR("TALER_CURRENCY_LEN_STR") NOT NULL"
 		   ",vsize VARCHAR NOT NULL"
+		   ",u16 INT2 NOT NULL"
+		   ",u32 INT4 NOT NULL"
+		   ",u64 INT8 NOT NULL"
+		   ",json VARCHAR NOT NULL"
 		   ")");
   if (PGRES_COMMAND_OK != PQresultStatus (result))
   {