diff --git a/chunk-format.c b/chunk-format.c
index 8d910e23f6..09ef86afa6 100644
--- a/chunk-format.c
+++ b/chunk-format.c
@@ -102,7 +102,8 @@ int read_table_of_contents(struct chunkfile *cf,
 			   const unsigned char *mfile,
 			   size_t mfile_size,
 			   uint64_t toc_offset,
-			   int toc_length)
+			   int toc_length,
+			   unsigned expected_alignment)
 {
 	int i;
 	uint32_t chunk_id;
@@ -120,6 +121,11 @@ int read_table_of_contents(struct chunkfile *cf,
 			error(_("terminating chunk id appears earlier than expected"));
 			return 1;
 		}
+		if (chunk_offset % expected_alignment != 0) {
+			error(_("chunk id %"PRIx32" not %d-byte aligned"),
+			      chunk_id, expected_alignment);
+			return 1;
+		}
 
 		table_of_contents += CHUNK_TOC_ENTRY_SIZE;
 		next_chunk_offset = get_be64(table_of_contents + 4);
diff --git a/chunk-format.h b/chunk-format.h
index 8dce7967f4..d608b8135c 100644
--- a/chunk-format.h
+++ b/chunk-format.h
@@ -36,7 +36,8 @@ int read_table_of_contents(struct chunkfile *cf,
 			   const unsigned char *mfile,
 			   size_t mfile_size,
 			   uint64_t toc_offset,
-			   int toc_length);
+			   int toc_length,
+			   unsigned expected_alignment);
 
 #define CHUNK_NOT_FOUND (-2)
 
diff --git a/commit-graph.c b/commit-graph.c
index b217e19194..472332f603 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -417,7 +417,7 @@ struct commit_graph *parse_commit_graph(struct repo_settings *s,
 	cf = init_chunkfile(NULL);
 
 	if (read_table_of_contents(cf, graph->data, graph_size,
-				   GRAPH_HEADER_SIZE, graph->num_chunks))
+				   GRAPH_HEADER_SIZE, graph->num_chunks, 1))
 		goto free_and_return;
 
 	read_chunk(cf, GRAPH_CHUNKID_OIDFANOUT, graph_read_oid_fanout, graph);
diff --git a/midx.c b/midx.c
index ec585cae1b..98f84fbe61 100644
--- a/midx.c
+++ b/midx.c
@@ -154,7 +154,8 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 	cf = init_chunkfile(NULL);
 
 	if (read_table_of_contents(cf, m->data, midx_size,
-				   MIDX_HEADER_SIZE, m->num_chunks))
+				   MIDX_HEADER_SIZE, m->num_chunks,
+				   MIDX_CHUNK_ALIGNMENT))
 		goto cleanup_fail;
 
 	if (pair_chunk(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names, &m->chunk_pack_names_len))
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 0a0ccec8a4..34f5944142 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -1094,4 +1094,18 @@ test_expect_success 'reader notices too-small pack names chunk' '
 	test_cmp expect err
 '
 
+test_expect_success 'reader handles unaligned chunks' '
+	# A 9-byte PNAM means all of the subsequent chunks
+	# will no longer be 4-byte aligned, but it is still
+	# a valid one-pack chunk on its own (it is "foo.pack\0").
+	corrupt_chunk PNAM clear 666f6f2e7061636b00 &&
+	git -c core.multipackindex=false log >expect.out &&
+	git -c core.multipackindex=true log >out 2>err &&
+	test_cmp expect.out out &&
+	cat >expect.err <<-\EOF &&
+	error: chunk id 4f494446 not 4-byte aligned
+	EOF
+	test_cmp expect.err err
+'
+
 test_done