diff --git a/pack-bitmap.c b/pack-bitmap.c
index fe5647e72e..074d9ac8f2 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -153,14 +153,18 @@ static int load_bitmap_header(struct bitmap_index *index)
 	/* Parse known bitmap format options */
 	{
 		uint32_t flags = ntohs(header->options);
+		size_t cache_size = st_mult(index->pack->num_objects, sizeof(uint32_t));
+		unsigned char *index_end = index->map + index->map_size - the_hash_algo->rawsz;
 
 		if ((flags & BITMAP_OPT_FULL_DAG) == 0)
 			return error("Unsupported options for bitmap index file "
 				"(Git requires BITMAP_OPT_FULL_DAG)");
 
 		if (flags & BITMAP_OPT_HASH_CACHE) {
-			unsigned char *end = index->map + index->map_size - the_hash_algo->rawsz;
-			index->hashes = ((uint32_t *)end) - index->pack->num_objects;
+			if (cache_size > index_end - index->map - header_size)
+				return error("corrupted bitmap index file (too short to fit hash cache)");
+			index->hashes = (void *)(index_end - cache_size);
+			index_end -= cache_size;
 		}
 	}
 
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index 8318781d2b..e2c3907a68 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -343,7 +343,8 @@ test_expect_success 'pack reuse respects --incremental' '
 	test_must_be_empty actual
 '
 
-test_expect_success 'truncated bitmap fails gracefully' '
+test_expect_success 'truncated bitmap fails gracefully (ewah)' '
+	test_config pack.writebitmaphashcache false &&
 	git repack -ad &&
 	git rev-list --use-bitmap-index --count --all >expect &&
 	bitmap=$(ls .git/objects/pack/*.bitmap) &&
@@ -352,7 +353,19 @@ test_expect_success 'truncated bitmap fails gracefully' '
 	mv -f $bitmap.tmp $bitmap &&
 	git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
 	test_cmp expect actual &&
-	test_i18ngrep corrupt stderr
+	test_i18ngrep corrupt.ewah.bitmap stderr
+'
+
+test_expect_success 'truncated bitmap fails gracefully (cache)' '
+	git repack -ad &&
+	git rev-list --use-bitmap-index --count --all >expect &&
+	bitmap=$(ls .git/objects/pack/*.bitmap) &&
+	test_when_finished "rm -f $bitmap" &&
+	test_copy_bytes 512 <$bitmap >$bitmap.tmp &&
+	mv -f $bitmap.tmp $bitmap &&
+	git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
+	test_cmp expect actual &&
+	test_i18ngrep corrupted.bitmap.index stderr
 '
 
 # have_delta <obj> <expected_base>