diff --git a/src/clientget.cpp b/src/clientget.cpp
index 682ff78..d037974 100644
--- a/src/clientget.cpp
+++ b/src/clientget.cpp
@@ -172,8 +172,8 @@ struct GPROp : public OperationBase
     {
         decltype (done) junk;
         decltype (onInit) junkI;
-        bool ret;
-        loop.call([this, &junk, &junkI, &ret](){
+        bool ret = false;
+        (void)loop.tryCall([this, &junk, &junkI, &ret](){
             ret = _cancel(false);
             junk = std::move(done);
             junkI = std::move(onInit);
diff --git a/src/clientintrospect.cpp b/src/clientintrospect.cpp
index ae2e48b..9f713a8 100644
--- a/src/clientintrospect.cpp
+++ b/src/clientintrospect.cpp
@@ -43,7 +43,7 @@ struct InfoOp : public OperationBase
     virtual bool cancel() override final {
         decltype (done) junk;
         bool ret = false;
-        loop.call([this, &junk, &ret](){
+        (void)loop.tryCall([this, &junk, &ret](){
             ret = _cancel(false);
             junk = std::move(done);
             // leave opByIOID for GC
diff --git a/src/clientmon.cpp b/src/clientmon.cpp
index f4e82bb..b76ce6b 100644
--- a/src/clientmon.cpp
+++ b/src/clientmon.cpp
@@ -187,8 +187,8 @@ struct SubscriptionImpl : public OperationBase, public Subscription
 
     virtual bool cancel() override final {
         decltype (event) junk;
-        bool ret;
-        loop.call([this, &junk, &ret](){
+        bool ret = false;
+        (void)loop.tryCall([this, &junk, &ret](){
             ret = _cancel(false);
             junk = std::move(event);
             // leave opByIOID for GC