diff --git a/pyproject.toml b/pyproject.toml
index 7bb5162..6b25d9e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -48,3 +48,7 @@ include = ["q2_feature_table*"]
 
 [tool.setuptools.package-data]
 q2_feature_table = ["**/*"]
+
+[tool.mutmut]
+paths_to_mutate = [ "q2_feature_table/" ]
+do_not_mutate = [ "**/tests/*", "*/__init__.py", "*/_version.py" ]
diff --git a/q2_feature_table/_core_features/_visualizer.py b/q2_feature_table/_core_features/_visualizer.py
index 0f38ee8..72140e5 100644
--- a/q2_feature_table/_core_features/_visualizer.py
+++ b/q2_feature_table/_core_features/_visualizer.py
@@ -20,7 +20,7 @@
     'q2_feature_table') / '_core_features' / 'core_features_assets'
 
 
-def core_features(output_dir, table: biom.Table, min_fraction: float = 0.5,
+def core_features(output_dir, table: biom.Table, min_fraction: float = 1.5,
                   max_fraction: float = 1.0, steps: int = 11) -> None:
     if max_fraction < min_fraction:
         raise ValueError('min_fraction (%r) parameter must be less than '
diff --git a/q2_feature_table/_normalize.py b/q2_feature_table/_normalize.py
index 98d5f33..5a9794c 100644
--- a/q2_feature_table/_normalize.py
+++ b/q2_feature_table/_normalize.py
@@ -45,7 +45,7 @@ def normalize(
 ) -> pd.DataFrame:
     # Validate parameter combinations and set trim parameters
     m_trim, a_trim = _validate_parameters(
-        method, m_trim, a_trim, gene_length)
+        method, None, a_trim, gene_length)
 
     # Process gene_lengths input and define methods that need gene_lengths
     # input