diff --git a/CHANGELOG.md b/CHANGELOG.md
index e9a8396c..1b72a557 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+# task_predict_modality 0.2.0
+
+## NEW FUNCTIONALITY
+
+* `scripts/create_datasets`: Trim mod1's features when generating the test resources, so the two modalities differ in width. The common test datasets are square (134 x 134, 1500 x 1500), which let dimension mix-ups pass `viash test` (PR #51).
+
 # task_predict_modality 0.1.1
 
 ## NEW FUNCTIONALITY
diff --git a/scripts/create_datasets/test_resources.sh b/scripts/create_datasets/test_resources.sh
index 7c00b7f8..bd8f9206 100755
--- a/scripts/create_datasets/test_resources.sh
+++ b/scripts/create_datasets/test_resources.sh
@@ -27,6 +27,15 @@ nextflow run . \
   --publish_dir "$OUTPUT_DIR" \
   --output_state '$id/state.yaml'
 
+# The common test datasets are square (134 x 134, 1500 x 1500), so a component can
+# mix up n_vars(mod1) and n_vars(mod2) and still pass viash test. Trim mod1 so the
+# fixture looks like a real dataset, where the two modalities differ in width.
+echo "Trim mod1 features"
+for name in bmmc_cite/normal bmmc_cite/swap bmmc_multiome/normal bmmc_multiome/swap; do
+  python scripts/create_datasets/trim_mod1_features.py \
+    "$OUTPUT_DIR/openproblems_neurips2021/$name"
+done
+
 echo "Run one method"
 
 for name in bmmc_cite/normal bmmc_cite/swap bmmc_multiome/normal bmmc_multiome/swap; do
diff --git a/scripts/create_datasets/trim_mod1_features.py b/scripts/create_datasets/trim_mod1_features.py
new file mode 100755
index 00000000..bf0f6329
--- /dev/null
+++ b/scripts/create_datasets/trim_mod1_features.py
@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+"""Trim mod1 to fewer features than mod2 in the generated test resources.
+
+The common test datasets happen to be square -- bmmc_cite is 134 x 134 and
+bmmc_multiome 1500 x 1500 -- so in resources_test a component can confuse
+n_vars(mod1) with n_vars(mod2) and still pass `viash test`. That is not true of
+any real dataset, where e.g. GEX has ~13953 features against 134 ADT proteins.
+
+Dropping a slice of mod1's features restores the asymmetry, so dimension
+mix-ups fail in CI rather than on the first full run.
+"""
+
+import sys
+from pathlib import Path
+
+import anndata as ad
+
+# keep this fraction of mod1's features
+KEEP_FRACTION = 0.75
+
+
+def trim(path: Path) -> None:
+    adata = ad.read_h5ad(path)
+    n_keep = int(adata.n_vars * KEEP_FRACTION)
+    trimmed = adata[:, :n_keep].copy()
+    trimmed.write_h5ad(path, compression="gzip")
+    print(f"  {path}: {adata.n_vars} -> {trimmed.n_vars} features", flush=True)
+
+
+def main(dataset_dir: str) -> None:
+    for name in ["train_mod1.h5ad", "test_mod1.h5ad"]:
+        trim(Path(dataset_dir) / name)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1])