diff --git a/fsck-cache.c b/fsck-cache.c
index a8050f84a9..b8b66d7d1d 100644
--- a/fsck-cache.c
+++ b/fsck-cache.c
@@ -17,33 +17,33 @@ static void check_connectivity(void)
 		struct revision *rev = revs[i];
 
 		if (show_unreachable && !(rev->flags & REACHABLE)) {
-			printf("unreachable %s\n", sha1_to_hex(rev->sha1));
+			printf("unreachable %s %s\n", rev->tag, sha1_to_hex(rev->sha1));
 			continue;
 		}
 
 		switch (rev->flags & (SEEN | USED)) {
 		case 0:
-			printf("bad %s\n", sha1_to_hex(rev->sha1));
+			printf("bad %s %s\n", rev->tag, sha1_to_hex(rev->sha1));
 			break;
 		case USED:
-			printf("missing %s\n", sha1_to_hex(rev->sha1));
+			printf("missing %s, %s\n", rev->tag, sha1_to_hex(rev->sha1));
 			break;
 		case SEEN:
-			printf("dangling %s\n", sha1_to_hex(rev->sha1));
+			printf("dangling %s %s\n", rev->tag, sha1_to_hex(rev->sha1));
 			break;
 		}
 	}
 }
 
-static void mark_needs_sha1(unsigned char *parent, const char * tag, unsigned char *child)
+static void mark_needs_sha1(unsigned char *parent, const char *ptag, unsigned char *child, const char *ctag)
 {
-	struct revision * child_rev = add_relationship(lookup_rev(parent), child);
+	struct revision * child_rev = add_relationship(lookup_rev(parent, ptag), child, ctag);
 	child_rev->flags |= USED;
 }
 
-static int mark_sha1_seen(unsigned char *sha1, char *tag)
+static int mark_sha1_seen(unsigned char *sha1, const char *tag)
 {
-	struct revision *rev = lookup_rev(sha1);
+	struct revision *rev = lookup_rev(sha1, tag);
 
 	rev->flags |= SEEN;
 	return 0;
@@ -69,7 +69,7 @@ static int fsck_tree(unsigned char *sha1, void *data, unsigned long size)
 
 		data += len + 20;
 		size -= len + 20;
-		mark_needs_sha1(sha1, S_ISDIR(mode) ? "tree" : "blob", file_sha1);
+		mark_needs_sha1(sha1, "tree", file_sha1, S_ISDIR(mode) ? "tree" : "blob");
 	}
 	return 0;
 }
@@ -84,13 +84,13 @@ static int fsck_commit(unsigned char *sha1, void *data, unsigned long size)
 		return -1;
 	if (get_sha1_hex(data + 5, tree_sha1) < 0)
 		return -1;
-	mark_needs_sha1(sha1, "tree", tree_sha1);
+	mark_needs_sha1(sha1, "commit", tree_sha1, "tree");
 	data += 5 + 40 + 1;	/* "tree " + <hex sha1> + '\n' */
 	parents = 0;
 	while (!memcmp(data, "parent ", 7)) {
 		if (get_sha1_hex(data + 7, parent_sha1) < 0)
 			return -1;
-		mark_needs_sha1(sha1, "commit", parent_sha1);
+		mark_needs_sha1(sha1, "commit", parent_sha1, "commit");
 		data += 7 + 40 + 1; 	/* "parent " + <hex sha1> + '\n' */
 		parents++;
 	}
@@ -186,7 +186,7 @@ int main(int argc, char **argv)
 			continue;
 		}
 		if (!get_sha1_hex(argv[i], head_sha1)) {
-			mark_reachable(lookup_rev(head_sha1), REACHABLE);
+			mark_reachable(lookup_rev(head_sha1, "commit"), REACHABLE);
 			heads++;
 			continue;
 		}
diff --git a/rev-tree.c b/rev-tree.c
index fe114ab360..3c54769258 100644
--- a/rev-tree.c
+++ b/rev-tree.c
@@ -37,7 +37,7 @@ static void read_cache_file(const char *path)
 			break;
 		if (get_sha1_hex(buf+1, sha1))
 			break;
-		rev = lookup_rev(sha1);
+		rev = lookup_rev(sha1, "commit");
 		rev->flags |= SEEN;
 		rev->date = date;
 
@@ -46,7 +46,7 @@ static void read_cache_file(const char *path)
 			unsigned char parent[20];
 			if (get_sha1_hex(buf + 1, parent))
 				break;
-			add_relationship(rev, parent);
+			add_relationship(rev, parent, "commit");
 		}
 	}
 	fclose(file);
@@ -127,7 +127,7 @@ int main(int argc, char **argv)
 	 * Now we have the maximal tree. Walk the different sha files back to the root.
 	 */
 	for (i = 0; i < nr; i++)
-		mark_reachable(lookup_rev(sha1[i]), 1 << i);
+		mark_reachable(lookup_rev(sha1[i], "commit"), 1 << i);
 
 	/*
 	 * Now print out the results..
diff --git a/revision.h b/revision.h
index 482729575c..7791a72e0a 100644
--- a/revision.h
+++ b/revision.h
@@ -25,6 +25,7 @@ struct revision {
 	unsigned char sha1[20];
 	unsigned long date;
 	struct parent *parent;
+	char tag[1];
 };
 
 static struct revision **revs;
@@ -51,13 +52,17 @@ static int find_rev(unsigned char *sha1)
 	return -first-1;
 }
 
-static struct revision *lookup_rev(unsigned char *sha1)
+static struct revision *lookup_rev(unsigned char *sha1, const char *tag)
 {
 	int pos = find_rev(sha1);
 	struct revision *n;
 
-	if (pos >= 0)
-		return revs[pos];
+	if (pos >= 0) {
+		n = revs[pos];
+		if (strcmp(n->tag, tag))
+			error("expected tag %s on object %s: got %s", tag, sha1_to_hex(sha1), n->tag);
+		return n;
+	}
 	
 	pos = -pos-1;
 
@@ -65,11 +70,12 @@ static struct revision *lookup_rev(unsigned char *sha1)
 		rev_allocs = alloc_nr(rev_allocs);
 		revs = realloc(revs, rev_allocs * sizeof(struct revision *));
 	}
-	n = malloc(sizeof(struct revision));
+	n = malloc(sizeof(struct revision) + strlen(tag));
 
 	n->flags = 0;
 	memcpy(n->sha1, sha1, 20);
 	n->parent = NULL;
+	strcpy(n->tag, tag);
 
 	/* Insert it into the right place */
 	memmove(revs + pos + 1, revs + pos, (nr_revs - pos) * sizeof(struct revision *));
@@ -79,9 +85,9 @@ static struct revision *lookup_rev(unsigned char *sha1)
 	return n;
 }
 
-static struct revision *add_relationship(struct revision *rev, unsigned char *needs)
+static struct revision *add_relationship(struct revision *rev, unsigned char *needs, const char *tag)
 {
-	struct revision *parent_rev = lookup_rev(needs);
+	struct revision *parent_rev = lookup_rev(needs, tag);
 	struct parent **pp = &rev->parent, *p;
 
 	while ((p = *pp) != NULL) {
@@ -131,7 +137,7 @@ static unsigned long parse_commit_date(const char *buf)
 
 static struct revision * parse_commit(unsigned char *sha1)
 {
-	struct revision *rev = lookup_rev(sha1);
+	struct revision *rev = lookup_rev(sha1, "commit");
 
 	if (!(rev->flags & SEEN)) {
 		void *buffer, *bufptr;
@@ -145,7 +151,7 @@ static struct revision * parse_commit(unsigned char *sha1)
 			die("%s is not a commit object", sha1_to_hex(sha1));
 		bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 		while (!memcmp(bufptr, "parent ", 7) && !get_sha1_hex(bufptr+7, parent)) {
-			add_relationship(rev, parent);
+			add_relationship(rev, parent, "commit");
 			parse_commit(parent);
 			bufptr += 48;	/* "parent " + "hex sha1" + "\n" */
 		}