diff --git a/sourmash_lib/lca/lca_utils.py b/sourmash_lib/lca/lca_utils.py
index fcdca0dc27..ffe8a8e93c 100644
--- a/sourmash_lib/lca/lca_utils.py
+++ b/sourmash_lib/lca/lca_utils.py
@@ -138,7 +138,10 @@ def load(self, db_name):
             xopen = gzip.open
 
         with xopen(db_name, 'rt') as fp:
-            load_d = json.load(fp)
+            try:
+                load_d = json.load(fp)
+            except json.decoder.JSONDecodeError:
+                raise ValueError("cannot parse database file '{}'; is it a valid LCA db?".format(db_name))
             version = load_d['version']
             assert version == '1.0'