diff --git a/src/objective-c/GRPCClient/private/GRPCChannel.m b/src/objective-c/GRPCClient/private/GRPCChannel.m
index fc0448bb962..52dacad9f50 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannel.m
+++ b/src/objective-c/GRPCClient/private/GRPCChannel.m
@@ -84,7 +84,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
 
   NSString *userAgent = @"grpc-objc/" GRPC_OBJC_VERSION_STRING;
   NSString *userAgentPrefix = _callOptions.userAgentPrefix;
-  if (userAgentPrefix) {
+  if (userAgentPrefix.length != 0) {
     args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] =
         [_callOptions.userAgentPrefix stringByAppendingFormat:@" %@", userAgent];
   } else {
@@ -242,7 +242,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
     if (self->_disconnected) {
       isDisconnected = YES;
     } else {
-      GRPCAssert(self->_unmanagedChannel != NULL, NSInvalidArgumentException, @"Invalid channel.");
+      GRPCAssert(self->_unmanagedChannel != NULL, NSInternalInconsistencyException, @"Channel should have valid unmanaged channel.");
 
       NSString *serverAuthority =
           callOptions.transportType == GRPCTransportTypeCronet ? nil : callOptions.serverAuthority;
@@ -281,14 +281,17 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
 
 // This function should be called on _dispatchQueue.
 - (void)ref {
-  _refcount++;
-  if (_refcount == 1 && _lastDispatch != nil) {
-    _lastDispatch = nil;
-  }
+  dispatch_sync(_dispatchQueue, ^{
+    self->_refcount++;
+    if (self->_refcount == 1 && self->_lastDispatch != nil) {
+      self->_lastDispatch = nil;
+    }
+  });
 }
 
 - (void)unref {
   dispatch_async(_dispatchQueue, ^{
+    GRPCAssert(self->_refcount > 0, NSInternalInconsistencyException, @"Illegal reference count.");
     self->_refcount--;
     if (self->_refcount == 0 && !self->_disconnected) {
       // Start timer.
@@ -298,7 +301,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
       self->_lastDispatch = now;
       dispatch_after(delay, self->_dispatchQueue, ^{
         // Timed disconnection.
-        if (self->_lastDispatch == now) {
+        if (!self->_disconnected && self->_lastDispatch == now) {
           grpc_channel_destroy(self->_unmanagedChannel);
           self->_unmanagedChannel = NULL;
           self->_disconnected = YES;
diff --git a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
index 2358c7bb0a8..f3fe8bac455 100644
--- a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
+++ b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
@@ -30,6 +30,7 @@
 #import "NSData+GRPC.h"
 #import "NSDictionary+GRPC.h"
 #import "NSError+GRPC.h"
+#import "utilities.h"
 
 #import "GRPCOpBatchLog.h"
 
@@ -248,16 +249,14 @@
 - (instancetype)initWithHost:(NSString *)host
                         path:(NSString *)path
                  callOptions:(GRPCCallOptions *)callOptions {
-  if (host.length == 0 || path.length == 0) {
-    [NSException raise:NSInvalidArgumentException format:@"path and host cannot be nil."];
-  }
+  GRPCAssert(host.length != 0 && path.length != 0, NSInvalidArgumentException, @"path and host cannot be nil.");
 
   if ((self = [super init])) {
     // Each completion queue consumes one thread. There's a trade to be made between creating and
     // consuming too many threads and having contention of multiple calls in a single completion
     // queue. Currently we use a singleton queue.
     _queue = [GRPCCompletionQueue completionQueue];
-    BOOL disconnected;
+    BOOL disconnected = NO;
     do {
       _channel = [[GRPCChannelPool sharedInstance] channelWithHost:host callOptions:callOptions];
       if (_channel == nil) {