diff --git a/funannotate2/predict.py b/funannotate2/predict.py
index e78a423..fd1ca64 100755
--- a/funannotate2/predict.py
+++ b/funannotate2/predict.py
@@ -34,8 +34,8 @@
 )
 from .log import finishLogging, startLogging, system_info
 from .utilities import (
+    busco_lineage_from_taxonomy,
     checkfile,
-    choose_best_busco_species,
     create_directories,
     create_tmpdir,
     ensure_busco_lineage,
@@ -903,10 +903,15 @@ def sort_gff_line(line):
         logger.warning(
             "Unable to access JGI taxonomy lookup, reverting to taxonomy from training data"
         )
-        taxonomy = params["taxonomy"]
-    busco_tax = choose_best_busco_species(
-        {"superkingdom": taxonomy.get("superkingdom"), "kingdom": taxonomy.get("kingdom")}
-    )
+        taxonomy = params.get("taxonomy")
+    busco_tax = busco_lineage_from_taxonomy(taxonomy, default=None)
+    if busco_tax is None:
+        busco_tax = "fungi"
+        logger.warning(
+            f"Could not resolve a BUSCO lineage for species '{args.species}' "
+            f"(taxonomy unavailable or unrecognized); defaulting to '{busco_tax}'. "
+            "BUSCO completeness scoring will be unreliable for a non-fungal genome."
+        )
     busco_model_path = ensure_busco_lineage(busco_tax, logger)
 
     # now we can loop through the abinitio predictions and run busco for completion
diff --git a/funannotate2/utilities.py b/funannotate2/utilities.py
index 4014ab2..b4a9d54 100755
--- a/funannotate2/utilities.py
+++ b/funannotate2/utilities.py
@@ -497,6 +497,53 @@ def choose_best_busco_species(query_tax):
     return best_taxonomy(query_tax, busco_taxonomy, exact=True)
 
 
+def busco_lineage_from_taxonomy(taxonomy, default="fungi"):
+    """
+    Resolve a valid BUSCO lineage key from a taxonomy dict, deterministically.
+
+    `predict` gets taxonomy from `lookup_taxonomy` (which returns False when the
+    JGI lookup fails) and falls back to the training-data taxonomy (which may
+    also be False for a novel organism). Passing such a value straight into
+    `choose_best_busco_species` either crashed (`.get()` on a bool) or, for a
+    non-empty but unmatched taxonomy, returned a random lineage via
+    `best_taxonomy`'s tie-break. This helper guards both cases and always returns
+    a lineage that exists in `busco_taxonomy`.
+
+    Parameters:
+    - taxonomy (dict or None): a taxonomy dict, or a falsy value (False/None) when unavailable.
+    - default (str): lineage to fall back to; must be a valid busco_taxonomy key.
+
+    Returns:
+    - str: a lineage key guaranteed to be present in busco_taxonomy.
+    """
+    if not isinstance(taxonomy, dict) or not taxonomy:
+        return default
+    query = {
+        "superkingdom": taxonomy.get("superkingdom"),
+        "kingdom": taxonomy.get("kingdom"),
+    }
+
+    # best_taxonomy() falls back to a random tie-break when nothing matches, and
+    # that random pick is always itself a valid busco_taxonomy key -- so a plain
+    # "result not in busco_taxonomy" check can never catch it. Only trust the
+    # matcher when the query actually overlaps the reference on superkingdom or
+    # kingdom; otherwise return the default deterministically.
+    def _overlaps(level):
+        value = query.get(level)
+        if not isinstance(value, str):
+            return False
+        value = value.lower()
+        return any(
+            isinstance(ref.get(level), str) and ref[level].lower() == value
+            for ref in busco_taxonomy.values()
+        )
+
+    if not (_overlaps("superkingdom") or _overlaps("kingdom")):
+        return default
+    lineage = choose_best_busco_species(query)
+    return lineage if lineage in busco_taxonomy else default
+
+
 def best_taxonomy(query, reference, exact=False):
     """
     Find the best matching taxonomy in a reference dictionary based on a query taxonomy.
diff --git a/tests/unit/test_utilities_taxonomy.py b/tests/unit/test_utilities_taxonomy.py
index f8ccb42..d553550 100644
--- a/tests/unit/test_utilities_taxonomy.py
+++ b/tests/unit/test_utilities_taxonomy.py
@@ -5,7 +5,10 @@
 from unittest.mock import patch
 
 import funannotate2.utilities
-from funannotate2.utilities import choose_best_busco_species
+from funannotate2.utilities import (
+    busco_lineage_from_taxonomy,
+    choose_best_busco_species,
+)
 from funannotate2.config import busco_taxonomy
 
 
@@ -351,3 +354,116 @@ def test_returns_valid_busco_key_always(self):
                 assert result in busco_taxonomy, (
                     f"Result '{result}' should be a valid key in busco_taxonomy"
                 )
+
+
+class TestBuscoLineageFromTaxonomy:
+    """Tests for busco_lineage_from_taxonomy.
+
+    Regression coverage for issue #93 (crash on missing taxonomy) plus the
+    latent random-lineage path: a non-empty taxonomy that matches nothing in
+    busco_taxonomy must resolve to the default deterministically, not to a
+    random tie-broken lineage.
+    """
+
+    def test_false_returns_default_without_crashing(self):
+        # Issue #93: predict() fed a `False` taxonomy straight into `.get()`,
+        # raising `AttributeError: 'bool' object has no attribute 'get'`.
+        assert busco_lineage_from_taxonomy(False) == "fungi"
+
+    def test_none_returns_default(self):
+        assert busco_lineage_from_taxonomy(None) == "fungi"
+
+    def test_empty_dict_returns_default(self):
+        assert busco_lineage_from_taxonomy({}) == "fungi"
+
+    def test_real_match_returns_valid_lineage(self):
+        # Exact, deterministic match -- not merely "some valid key", which would
+        # also pass if _overlaps() regressed and everything silently defaulted.
+        result = busco_lineage_from_taxonomy(
+            {"superkingdom": "Eukaryota", "kingdom": "Fungi"}
+        )
+        assert result == "fungi"
+
+    def test_partial_but_matching_dict_returns_valid_lineage(self):
+        # superkingdom-only match resolves to the broad "eukaryota" lineage.
+        result = busco_lineage_from_taxonomy({"superkingdom": "Eukaryota"})
+        assert result == "eukaryota"
+
+    def test_non_matching_dict_is_deterministic_default(self):
+        # A non-empty dict whose values match nothing would otherwise fall
+        # through best_taxonomy to random.choice(); the helper must not.
+        results = {
+            busco_lineage_from_taxonomy(
+                {"superkingdom": "Bacteria", "kingdom": "Nonexistent"}
+            )
+            for _ in range(50)
+        }
+        assert results == {"fungi"}
+
+    def test_all_none_is_deterministic_default(self):
+        results = {
+            busco_lineage_from_taxonomy({"superkingdom": None, "kingdom": None})
+            for _ in range(50)
+        }
+        assert results == {"fungi"}
+
+    def test_result_is_always_a_valid_lineage(self):
+        inputs = [
+            False,
+            None,
+            {},
+            {"superkingdom": "Eukaryota", "kingdom": "Fungi"},
+            {"superkingdom": "Eukaryota"},
+            {"superkingdom": "Bacteria", "kingdom": "Nonexistent"},
+        ]
+        for tax in inputs:
+            assert busco_lineage_from_taxonomy(tax) in busco_taxonomy
+
+    def test_default_none_signals_unresolved(self):
+        # predict() passes default=None to detect when it must warn and fall back.
+        assert busco_lineage_from_taxonomy(False, default=None) is None
+        assert (
+            busco_lineage_from_taxonomy(
+                {"superkingdom": "Bacteria", "kingdom": "Nonexistent"}, default=None
+            )
+            is None
+        )
+        # a genuine match still returns a real lineage, not the sentinel
+        assert (
+            busco_lineage_from_taxonomy(
+                {"superkingdom": "Eukaryota", "kingdom": "Fungi"}, default=None
+            )
+            in busco_taxonomy
+        )
+
+    def test_default_is_overridable(self):
+        assert (
+            busco_lineage_from_taxonomy(False, default="eukaryota") == "eukaryota"
+        )
+
+    def test_every_kingdom_resolves_deterministically(self):
+        # The determinism guarantee currently rests on the busco_taxonomy data
+        # shape, not on structure. Sweep every real kingdom with no superkingdom
+        # (the shape most likely to reach best_taxonomy's random tie-break) and
+        # assert a single stable result across many runs, so a future reference
+        # edit that reintroduces a random pick fails here instead of shipping.
+        kingdoms = {
+            v.get("kingdom") for v in busco_taxonomy.values() if v.get("kingdom")
+        }
+        for kingdom in kingdoms:
+            results = {
+                busco_lineage_from_taxonomy({"superkingdom": None, "kingdom": kingdom})
+                for _ in range(25)
+            }
+            assert len(results) == 1, f"non-deterministic lineage for {kingdom}: {results}"
+            assert results.pop() in busco_taxonomy
+
+    def test_non_string_values_do_not_crash(self):
+        # Guards the isinstance(value, str) checks in _overlaps: odd taxonomy
+        # values must degrade to a valid default, never raise.
+        for tax in [
+            {"superkingdom": 123, "kingdom": ["Fungi"]},
+            {"superkingdom": {"x": 1}, "kingdom": None},
+            {"superkingdom": "", "kingdom": ""},
+        ]:
+            assert busco_lineage_from_taxonomy(tax) in busco_taxonomy