I'm unable to reproduce this report on escher/unstable: $ g++ -c -fPIC -fno-rtti -fno-exceptions -gstabs -Wall -Wconversion -Wpointer-arith -Wcast-align -Woverloaded-virtual -Wsynth -Wno-ctor-dtor-privacy -Wno-long-long -O2 -mieee -fshort-wchar -pthread -pipe imgContainerGIF.ii In file included from imgContainerGIF.cpp:27: imgContainerGIF.h:115: error: syntax error before `)' token ../../../../dist/include/imglib2/imgIContainer.h:137: warning: `virtual nsresult imgIContainer::GetLoopCount(PRInt32*)' was hidden imgContainerGIF.h:115: warning: by `virtual nsresult imgContainerGIF::GetLoopCount(...)' imgContainerGIF.cpp: In member function `virtual nsresult imgContainerGIF::QueryInterface(const nsIID&, void**)': imgContainerGIF.cpp:36: error: `s' undeclared (first use this function) imgContainerGIF.cpp:36: error: (Each undeclared identifier is reported only once for each function it appears in.) imgContainerGIF.cpp:36: error: syntax error before `;' token imgContainerGIF.cpp: At global scope: imgContainerGIF.cpp:323: error: prototype for `nsresult imgContainerGIF::GetLoopCount(PRInt32*)' does not match any in class ` imgContainerGIF' imgContainerGIF.h:115: error: candidate is: virtual nsresult imgContainerGIF::GetLoopCount(...)