diff --git a/src/zap.c b/src/zap.c
index 127395788..e122a68eb 100644
--- a/src/zap.c
+++ b/src/zap.c
@@ -4089,6 +4089,11 @@ boomhit(struct obj *obj, coordxy dx, coordxy dy)
         dy = ydir[i];
         gb.bhitpos.x += dx;
         gb.bhitpos.y += dy;
+        if (!isok(gb.bhitpos.x, gb.bhitpos.y)) {
+            gb.bhitpos.x -= dx;
+            gb.bhitpos.y -= dy;
+            break;
+        }
         if ((mtmp = m_at(gb.bhitpos.x, gb.bhitpos.y)) != 0) {
             m_respond(mtmp);
             tmp_at(DISP_END, 0);