diff --git a/bw_processing/constants.py b/bw_processing/constants.py
index 09f102f..71ff749 100644
--- a/bw_processing/constants.py
+++ b/bw_processing/constants.py
@@ -4,6 +4,7 @@
 import numpy as np
 
 MAX_SIGNED_32BIT_INT = 2147483647
+MAX_SIGNED_64BIT_INT = 9223372036854775807
 
 # We could try to save space by not storing the columns
 # `row_index` and `col_index`, and add them after loading from
@@ -20,7 +21,7 @@
     ("maximum", np.float32),
     ("negative", bool),
 ]
-INDICES_DTYPE = [("row", np.int32), ("col", np.int32)]
+INDICES_DTYPE = [("row", np.int64), ("col", np.int64)]
 
 NAME_RE = re.compile(r"^[\w\-\.]*$")
 
diff --git a/bw_processing/datapackage.py b/bw_processing/datapackage.py
index 471a419..6daa686 100644
--- a/bw_processing/datapackage.py
+++ b/bw_processing/datapackage.py
@@ -14,6 +14,8 @@
 from .constants import (
     DEFAULT_LICENSES,
     INDICES_DTYPE,
+    MAX_SIGNED_32BIT_INT,
+    MAX_SIGNED_64BIT_INT,
     NUMPY_SERIALIZE_FORMAT_EXTENSION,
     NUMPY_SERIALIZE_FORMAT_NAME,
     PARQUET_SERIALIZE_FORMAT_EXTENSION,
@@ -257,6 +259,12 @@ def rehydrate_interface(
 
         self.data[index] = resource
 
+    def get_max_index_value(self) -> int:
+        """Get maximum index value (max signed 32 or 64 bit integer) for this datapackage"""
+        if self.metadata.get("64_bit_indices"):
+            return MAX_SIGNED_64BIT_INT
+        return MAX_SIGNED_32BIT_INT
+
 
 class FilteredDatapackage(DatapackageBase):
     """A subset of a datapackage. Used in matrix construction or other data manipulation operations.
@@ -360,6 +368,7 @@ def _create(
             "combinatorial": combinatorial,
             "sequential": sequential,
             "seed": seed,
+            "64_bit_indices": True,
             "sum_intra_duplicates": sum_intra_duplicates,
             "sum_inter_duplicates": sum_inter_duplicates,
             "matrix_serialize_format_type": matrix_serialize_format_type.value,
diff --git a/tests/fixtures/indexing/array.indices.npy b/tests/fixtures/indexing/array.indices.npy
index f8634de..3826c0f 100644
Binary files a/tests/fixtures/indexing/array.indices.npy and b/tests/fixtures/indexing/array.indices.npy differ
diff --git a/tests/fixtures/indexing/datapackage.json b/tests/fixtures/indexing/datapackage.json
index ecf1fe5..bbb230f 100644
--- a/tests/fixtures/indexing/datapackage.json
+++ b/tests/fixtures/indexing/datapackage.json
@@ -50,10 +50,10 @@
       "profile": "data-resource",
       "format": "npy",
       "mediatype": "application/octet-stream",
-      "name": "array.data",
+      "name": "array.indices",
       "matrix": "sa_matrix",
-      "kind": "data",
-      "path": "array.data.npy",
+      "kind": "indices",
+      "path": "array.indices.npy",
       "group": "array",
       "category": "array",
       "nrows": 3
@@ -62,10 +62,10 @@
       "profile": "data-resource",
       "format": "npy",
       "mediatype": "application/octet-stream",
-      "name": "array.indices",
+      "name": "array.data",
       "matrix": "sa_matrix",
-      "kind": "indices",
-      "path": "array.indices.npy",
+      "kind": "data",
+      "path": "array.data.npy",
       "group": "array",
       "category": "array",
       "nrows": 3
@@ -167,10 +167,11 @@
       ]
     }
   ],
-  "created": "2021-05-18T13:12:19.590666Z",
+  "created": "2024-08-18T20:58:57.736902Z",
   "combinatorial": false,
   "sequential": false,
   "seed": null,
   "sum_intra_duplicates": true,
-  "sum_inter_duplicates": false
-}
+  "sum_inter_duplicates": false,
+  "matrix_serialize_format_type": "numpy"
+}
\ No newline at end of file
diff --git a/tests/fixtures/indexing/vector.data.npy b/tests/fixtures/indexing/vector.data.npy
index abb6ffd..8c300fb 100644
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diff --git a/tests/fixtures/indexing/vector.indices.npy b/tests/fixtures/indexing/vector.indices.npy
index f8634de..3826c0f 100644
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diff --git a/tests/fixtures/merging/merging_first.zip b/tests/fixtures/merging/merging_first.zip
index 7182312..5d2425c 100644
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diff --git a/tests/fixtures/merging/merging_same_1.zip b/tests/fixtures/merging/merging_same_1.zip
index 6e7d713..61834c8 100644
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diff --git a/tests/fixtures/merging/merging_same_2.zip b/tests/fixtures/merging/merging_same_2.zip
index 0355738..feae666 100644
Binary files a/tests/fixtures/merging/merging_same_2.zip and b/tests/fixtures/merging/merging_same_2.zip differ
diff --git a/tests/fixtures/merging/merging_second.zip b/tests/fixtures/merging/merging_second.zip
index d239b5e..45041c4 100644
Binary files a/tests/fixtures/merging/merging_second.zip and b/tests/fixtures/merging/merging_second.zip differ
diff --git a/tests/fixtures/test-fixture.zip b/tests/fixtures/test-fixture.zip
index 7d4c1aa..4140734 100644
Binary files a/tests/fixtures/test-fixture.zip and b/tests/fixtures/test-fixture.zip differ
diff --git a/tests/fixtures/tfd/datapackage.json b/tests/fixtures/tfd/datapackage.json
index 9c04974..6cb5f94 100644
--- a/tests/fixtures/tfd/datapackage.json
+++ b/tests/fixtures/tfd/datapackage.json
@@ -203,7 +203,7 @@
       "valid_for": "sa-data-array"
     }
   ],
-  "created": "2024-05-22T12:20:16.587994+00:00Z",
+  "created": "2024-08-18T20:58:29.941013Z",
   "combinatorial": false,
   "sequential": false,
   "seed": null,
diff --git a/tests/fixtures/tfd/sa-array-interface.indices.npy b/tests/fixtures/tfd/sa-array-interface.indices.npy
index 08fa6ec..759389f 100644
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diff --git a/tests/fixtures/tfd/sa-data-array.indices.npy b/tests/fixtures/tfd/sa-data-array.indices.npy
index 08fa6ec..759389f 100644
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diff --git a/tests/fixtures/tfd/sa-data-vector-from-dict.indices.npy b/tests/fixtures/tfd/sa-data-vector-from-dict.indices.npy
index ad5e19f..b806140 100644
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diff --git a/tests/fixtures/tfd/sa-data-vector.indices.npy b/tests/fixtures/tfd/sa-data-vector.indices.npy
index 08fa6ec..759389f 100644
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diff --git a/tests/fixtures/tfd/sa-vector-interface.indices.npy b/tests/fixtures/tfd/sa-vector-interface.indices.npy
index 08fa6ec..759389f 100644
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