diff --git a/pittgoogle/alert.py b/pittgoogle/alert.py
index 1f7bca9..d805b78 100644
--- a/pittgoogle/alert.py
+++ b/pittgoogle/alert.py
@@ -295,9 +295,9 @@ def dataframe(self) -> "pd.DataFrame":
         import pandas as pd  # always lazy-load pandas. it hogs memory on cloud functions and run
 
         # sources and previous sources are expected to have the same fields
-        sources_df = pd.DataFrame([self.get("source")] + self.get("prv_sources"))
+        sources_df = pd.DataFrame([self.get("source")] + self.get("prv_sources", []))
         # sources and forced sources may have different fields
-        forced_df = pd.DataFrame(self.get("prv_forced_sources"))
+        forced_df = pd.DataFrame(self.get("prv_forced_sources", []))
 
         # use nullable integer data type to avoid converting ints to floats
         # for columns in one dataframe but not the other