File the break until it's flat, then carefully sand with sandpaper wrapped around a small, flat block of wood it until it's perfectly flat and smooth. Use a small block for sanding so you don't rock it. Get a piece of wood similar to the stock wood. Try to match the grain (it won't be perfect). Then sand the repair piece until it's flat and smooth, wipe the dust off the repair wood and stock, apply some Brownell's Acraglas (not the gel), and clamp the piece to the stock.
Let dry for 24 hours, then rasp and file the repair wood down to match the stock, sand smooth, stain, and finish. This all sounds harder than it actually is. The hardest part may be matching the stain but you can practice with scrap wood. Hope this helps.