diff --git a/swh/loader/package/nixguix/loader.py b/swh/loader/package/nixguix/loader.py
--- a/swh/loader/package/nixguix/loader.py
+++ b/swh/loader/package/nixguix/loader.py
@@ -196,7 +196,8 @@
         )
 
     # Only the version 1 is currently supported
-    if sources["version"] != 1:
+    version = int(sources["version"])
+    if version != 1:
         raise ValueError(
             "The sources structure version '%d' is not supported", sources["version"]
         )
diff --git a/swh/loader/package/nixguix/tests/data/https_nix-community.github.io/nixpkgs-swh_sources.json b/swh/loader/package/nixguix/tests/data/https_nix-community.github.io/nixpkgs-swh_sources.json
--- a/swh/loader/package/nixguix/tests/data/https_nix-community.github.io/nixpkgs-swh_sources.json
+++ b/swh/loader/package/nixguix/tests/data/https_nix-community.github.io/nixpkgs-swh_sources.json
@@ -11,6 +11,6 @@
       "integrity": "sha256-Q0copBCnj1b8G1iZw1k0NuYasMcx6QctleltspAgXlM="
     }
  ],
-    "version": 1,
+    "version": "1",
     "revision": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7"
 }
diff --git a/swh/loader/package/nixguix/tests/test_nixguix.py b/swh/loader/package/nixguix/tests/test_nixguix.py
--- a/swh/loader/package/nixguix/tests/test_nixguix.py
+++ b/swh/loader/package/nixguix/tests/test_nixguix.py
@@ -59,12 +59,16 @@
 
 
 def test_clean_sources_invalid_version(swh_config, requests_mock_datadir):
-    sources = {"version": 2, "sources": [], "revision": "my-revision"}
-
-    with pytest.raises(
-        ValueError, match="sources structure version .* is not supported"
-    ):
-        clean_sources(sources)
+    for version_ok in [1, "1"]:  # Check those versions are fine
+        clean_sources({"version": version_ok, "sources": [], "revision": "my-revision"})
+
+    for version_ko in [0, "0", 2, "2"]:  # Check version != 1 raise an error
+        with pytest.raises(
+            ValueError, match="sources structure version .* is not supported"
+        ):
+            clean_sources(
+                {"version": version_ko, "sources": [], "revision": "my-revision"}
+            )
 
 
 def test_clean_sources_invalid_sources(swh_config, requests_mock_datadir):