diff --git a/src/dogmove.c b/src/dogmove.c
index d0005ab78..f4c7b4bcb 100644
--- a/src/dogmove.c
+++ b/src/dogmove.c
@@ -316,9 +316,13 @@ dog_eat(struct monst *mtmp,
             edog->apport += (int) (200L / ((long) edog->dropdist + svm.moves
                                            - edog->droptime));
             if (edog->apport <= 0) {
-                impossible("dog_eat: pet apport <= 0 (%d, %d, %ld, %ld)",
+                impossible("dog_eat: pet apport <= 0 (%d, %d, %ld, %ld, %ud, %ud)",
                             edog->apport, edog->dropdist, edog->droptime,
-                            svm.moves);
+                            svm.moves,
+                           /* check whether edog struct got clobbered;
+                              these two values should always match if
+                              edog content is still intact */
+                           mtmp->m_id, edog->parentmid);
                 edog->apport = 1;
             }
         }