diff --git a/bw2io/strategies/simapro.py b/bw2io/strategies/simapro.py
index 0812b33..ead1ea8 100644
--- a/bw2io/strategies/simapro.py
+++ b/bw2io/strategies/simapro.py
@@ -215,6 +215,9 @@ def sp_allocate_products(db):
                         ds["parameters"] = {
                             k.lower(): v for k, v in ds["parameters"].items()
                         }
+                        for k in ds["parameters"].keys():
+                            if "formula" in ds["parameters"][k]:
+                                ds["parameters"][k]["formula"] = ds["parameters"][k]["formula"].lower()
                         interp = bw2parameters.ParameterSet(
                             ds["parameters"]
                         ).get_interpreter()