diff --git a/src/core/surface/call.c b/src/core/surface/call.c
index e18c0be107308aa3d60a1937b5a4673625a35543..e7d6c7d88c66a340fcf1d5df1e15caeab0e61e87 100644
--- a/src/core/surface/call.c
+++ b/src/core/surface/call.c
@@ -1187,7 +1187,7 @@ void grpc_call_destroy(grpc_call *c) {
 }
 
 grpc_call_error grpc_call_cancel(grpc_call *call, void *reserved) {
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   return grpc_call_cancel_with_status(call, GRPC_STATUS_CANCELLED, "Cancelled",
                                       NULL);
 }
@@ -1431,7 +1431,7 @@ grpc_call_error grpc_call_start_batch(grpc_call *call, const grpc_op *ops,
   const grpc_op *op;
   grpc_ioreq *req;
   void (*finish_func)(grpc_call *, int, void *) = finish_batch;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
 
   GRPC_CALL_LOG_BATCH(GPR_INFO, call, ops, nops, tag);
 
@@ -1446,6 +1446,7 @@ grpc_call_error grpc_call_start_batch(grpc_call *call, const grpc_op *ops,
   /* rewrite batch ops into ioreq ops */
   for (in = 0, out = 0; in < nops; in++) {
     op = &ops[in];
+    GPR_ASSERT(!op->reserved);
     switch (op->op) {
       case GRPC_OP_SEND_INITIAL_METADATA:
         /* Flag validation: currently allow no flags */
diff --git a/src/core/surface/channel.c b/src/core/surface/channel.c
index d16600d7c82c0cb2a3c521fc223a49da67e8ee79..1913aa1181c8f8bf6bd432675592ae21b894d158 100644
--- a/src/core/surface/channel.c
+++ b/src/core/surface/channel.c
@@ -155,7 +155,7 @@ grpc_call *grpc_channel_create_call(grpc_channel *channel,
                                     grpc_completion_queue *cq,
                                     const char *method, const char *host,
                                     gpr_timespec deadline, void *reserved) {
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   return grpc_channel_create_call_internal(
       channel, cq,
       grpc_mdelem_from_metadata_strings(
@@ -170,7 +170,7 @@ grpc_call *grpc_channel_create_call(grpc_channel *channel,
 void *grpc_channel_register_call(grpc_channel *channel, const char *method,
                                  const char *host, void *reserved) {
   registered_call *rc = gpr_malloc(sizeof(registered_call));
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   rc->path = grpc_mdelem_from_metadata_strings(
       channel->metadata_context, GRPC_MDSTR_REF(channel->path_string),
       grpc_mdstr_from_string(channel->metadata_context, method));
@@ -188,7 +188,7 @@ grpc_call *grpc_channel_create_registered_call(
     grpc_channel *channel, grpc_completion_queue *completion_queue,
     void *registered_call_handle, gpr_timespec deadline, void *reserved) {
   registered_call *rc = registered_call_handle;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   return grpc_channel_create_call_internal(
       channel, completion_queue, GRPC_MDELEM_REF(rc->path),
       GRPC_MDELEM_REF(rc->authority), deadline);
diff --git a/src/core/surface/channel_create.c b/src/core/surface/channel_create.c
index 44aacea6522d93d780c91e3de2a9e1e6e65ec3a5..89660a01daab3593e16384fadee2a67a5764dca5 100644
--- a/src/core/surface/channel_create.c
+++ b/src/core/surface/channel_create.c
@@ -161,7 +161,7 @@ grpc_channel *grpc_channel_create(const char *target,
   subchannel_factory *f;
   grpc_mdctx *mdctx = grpc_mdctx_create();
   int n = 0;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   /* TODO(census)
   if (grpc_channel_args_is_census_enabled(args)) {
     filters[n++] = &grpc_client_census_filter;
diff --git a/src/core/surface/completion_queue.c b/src/core/surface/completion_queue.c
index 82b5ff23c54dace0319c82dff66d24ce702c1739..d015b63718074701dead053c9ec4bdd8efb29b17 100644
--- a/src/core/surface/completion_queue.c
+++ b/src/core/surface/completion_queue.c
@@ -64,7 +64,7 @@ struct grpc_completion_queue {
 
 grpc_completion_queue *grpc_completion_queue_create(void *reserved) {
   grpc_completion_queue *cc = gpr_malloc(sizeof(grpc_completion_queue));
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   memset(cc, 0, sizeof(*cc));
   /* Initial ref is dropped by grpc_completion_queue_shutdown */
   gpr_ref_init(&cc->pending_events, 1);
@@ -149,7 +149,7 @@ grpc_event grpc_completion_queue_next(grpc_completion_queue *cc,
                                       gpr_timespec deadline,
                                       void *reserved) {
   grpc_event ret;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
 
   deadline = gpr_convert_clock_type(deadline, GPR_CLOCK_MONOTONIC);
 
@@ -192,7 +192,7 @@ grpc_event grpc_completion_queue_pluck(grpc_completion_queue *cc, void *tag,
   grpc_event ret;
   grpc_cq_completion *c;
   grpc_cq_completion *prev;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
 
   deadline = gpr_convert_clock_type(deadline, GPR_CLOCK_MONOTONIC);
 
diff --git a/src/core/surface/server.c b/src/core/surface/server.c
index ae53127b7c68e5375e370938dc8c168920fc6745..79ce3f6e1661697354406475311edd5bf9ae8ef3 100644
--- a/src/core/surface/server.c
+++ b/src/core/surface/server.c
@@ -729,7 +729,7 @@ void grpc_server_register_completion_queue(grpc_server *server,
                                            grpc_completion_queue *cq,
                                            void *reserved) {
   size_t i, n;
-  (void) reserved;
+  GPR_ASSERT(!reserved);
   for (i = 0; i < server->cq_count; i++) {
     if (server->cqs[i] == cq) return;
   }