Symbol lookup error at runtime even though nm reports symbol present

I build my program like this:

g++ -std=c++11 myprog.cpp -o myprog -lqpid-proton-cpp

Then I run ./myprog and get this error:

symbol lookup error: ./myprog: undefined symbol: _ZN6proton10event_loop6injectESt8functionIFvvEE

Yet, nm reports the symbol is present in the library . . .

nm -D /usr/lib/libqpid-proton-cpp.so | grep _ZN6proton10event_loop6injectESt8functionIFvvEE

. . . yields:

000000000002f460 T _ZN6proton10event_loop6injectESt8functionIFvvEE

What am I missing here?