diff --git a/commit-graph.c b/commit-graph.c
index 0aa1640d15..9e6eaa8a46 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -128,6 +128,16 @@ timestamp_t commit_graph_generation(const struct commit *c)
 	return GENERATION_NUMBER_INFINITY;
 }
 
+static timestamp_t commit_graph_generation_from_graph(const struct commit *c)
+{
+	struct commit_graph_data *data =
+		commit_graph_data_slab_peek(&commit_graph_data_slab, c);
+
+	if (!data || data->graph_pos == COMMIT_NOT_FROM_GRAPH)
+		return GENERATION_NUMBER_INFINITY;
+	return data->generation;
+}
+
 static struct commit_graph_data *commit_graph_data_at(const struct commit *c)
 {
 	unsigned int i, nth_slab;
@@ -2550,9 +2560,6 @@ static void graph_report(const char *fmt, ...)
 	va_end(ap);
 }
 
-#define GENERATION_ZERO_EXISTS 1
-#define GENERATION_NUMBER_EXISTS 2
-
 static int commit_graph_checksum_valid(struct commit_graph *g)
 {
 	return hashfile_checksum_valid(g->data, g->data_len);
@@ -2565,7 +2572,8 @@ static int verify_one_commit_graph(struct repository *r,
 {
 	uint32_t i, cur_fanout_pos = 0;
 	struct object_id prev_oid, cur_oid;
-	int generation_zero = 0;
+	struct commit *seen_gen_zero = NULL;
+	struct commit *seen_gen_non_zero = NULL;
 
 	verify_commit_graph_error = verify_commit_graph_lite(g);
 	if (verify_commit_graph_error)
@@ -2659,7 +2667,7 @@ static int verify_one_commit_graph(struct repository *r,
 					     oid_to_hex(&graph_parents->item->object.oid),
 					     oid_to_hex(&odb_parents->item->object.oid));
 
-			generation = commit_graph_generation(graph_parents->item);
+			generation = commit_graph_generation_from_graph(graph_parents->item);
 			if (generation > max_generation)
 				max_generation = generation;
 
@@ -2671,16 +2679,12 @@ static int verify_one_commit_graph(struct repository *r,
 			graph_report(_("commit-graph parent list for commit %s terminates early"),
 				     oid_to_hex(&cur_oid));
 
-		if (!commit_graph_generation(graph_commit)) {
-			if (generation_zero == GENERATION_NUMBER_EXISTS)
-				graph_report(_("commit-graph has generation number zero for commit %s, but non-zero elsewhere"),
-					     oid_to_hex(&cur_oid));
-			generation_zero = GENERATION_ZERO_EXISTS;
-		} else if (generation_zero == GENERATION_ZERO_EXISTS)
-			graph_report(_("commit-graph has non-zero generation number for commit %s, but zero elsewhere"),
-				     oid_to_hex(&cur_oid));
+		if (commit_graph_generation_from_graph(graph_commit))
+			seen_gen_non_zero = graph_commit;
+		else
+			seen_gen_zero = graph_commit;
 
-		if (generation_zero == GENERATION_ZERO_EXISTS)
+		if (seen_gen_zero)
 			continue;
 
 		/*
@@ -2706,6 +2710,12 @@ static int verify_one_commit_graph(struct repository *r,
 				     odb_commit->date);
 	}
 
+	if (seen_gen_zero && seen_gen_non_zero)
+		graph_report(_("commit-graph has both zero and non-zero "
+			       "generations (e.g., commits '%s' and '%s')"),
+			     oid_to_hex(&seen_gen_zero->object.oid),
+			     oid_to_hex(&seen_gen_non_zero->object.oid));
+
 	return verify_commit_graph_error;
 }
 
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 4df76173a8..ba65f17dd9 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -450,14 +450,15 @@ GRAPH_BYTE_FANOUT2=$(($GRAPH_FANOUT_OFFSET + 4 * 255))
 GRAPH_OID_LOOKUP_OFFSET=$(($GRAPH_FANOUT_OFFSET + 4 * 256))
 GRAPH_BYTE_OID_LOOKUP_ORDER=$(($GRAPH_OID_LOOKUP_OFFSET + $HASH_LEN * 8))
 GRAPH_BYTE_OID_LOOKUP_MISSING=$(($GRAPH_OID_LOOKUP_OFFSET + $HASH_LEN * 4 + 10))
+GRAPH_COMMIT_DATA_WIDTH=$(($HASH_LEN + 16))
 GRAPH_COMMIT_DATA_OFFSET=$(($GRAPH_OID_LOOKUP_OFFSET + $HASH_LEN * $NUM_COMMITS))
 GRAPH_BYTE_COMMIT_TREE=$GRAPH_COMMIT_DATA_OFFSET
 GRAPH_BYTE_COMMIT_PARENT=$(($GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN))
 GRAPH_BYTE_COMMIT_EXTRA_PARENT=$(($GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 4))
 GRAPH_BYTE_COMMIT_WRONG_PARENT=$(($GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 3))
 GRAPH_BYTE_COMMIT_GENERATION=$(($GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 11))
+GRAPH_BYTE_COMMIT_GENERATION_LAST=$(($GRAPH_BYTE_COMMIT_GENERATION + $(($NUM_COMMITS - 1)) * $GRAPH_COMMIT_DATA_WIDTH))
 GRAPH_BYTE_COMMIT_DATE=$(($GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 12))
-GRAPH_COMMIT_DATA_WIDTH=$(($HASH_LEN + 16))
 GRAPH_OCTOPUS_DATA_OFFSET=$(($GRAPH_COMMIT_DATA_OFFSET + \
 			     $GRAPH_COMMIT_DATA_WIDTH * $NUM_COMMITS))
 GRAPH_BYTE_OCTOPUS=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4))
@@ -596,11 +597,6 @@ test_expect_success 'detect incorrect generation number' '
 		"generation for commit"
 '
 
-test_expect_success 'detect incorrect generation number' '
-	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\01" \
-		"commit-graph generation for commit"
-'
-
 test_expect_success 'detect incorrect commit date' '
 	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_DATE "\01" \
 		"commit date"
@@ -622,6 +618,16 @@ test_expect_success 'detect incorrect chunk count' '
 		$GRAPH_CHUNK_LOOKUP_OFFSET
 '
 
+test_expect_success 'detect mixed generation numbers (non-zero to zero)' '
+	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION_LAST "\0\0\0\0" \
+		"both zero and non-zero generations"
+'
+
+test_expect_success 'detect mixed generation numbers (zero to non-zero)' '
+	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\0\0\0\0" \
+		"both zero and non-zero generations"
+'
+
 test_expect_success 'git fsck (checks commit-graph when config set to true)' '
 	git -C full fsck &&
 	corrupt_graph_and_verify $GRAPH_BYTE_FOOTER "\00" \