PVS-Studio warning V576 for Coin3D

unsigned int SbOctTreeNode::totalNumberOfItems(void) const;

void
SbOctTreeNode::debugTree(FILE *fp, const int indent) const
{
  ....
  (void)fprintf(fp, "%s, %d items, ",
    this->isLeaf() ? "Leaf" : "Group",
    this->totalNumberOfItems());
  ....
}

This suspicious code was found in Coin3D project by PVS-Studio static code analyzer.
Warning message is:
V576 Incorrect format. Consider checking the fourth actual argument of the 'fprintf' function. The SIGNED integer type argument is expected. sbocttree.cpp 214

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