diff --git a/src/ifctester/ifctester/__main__.py b/src/ifctester/ifctester/__main__.py
index a61e2e0b7d..b9ab913813 100644
--- a/src/ifctester/ifctester/__main__.py
+++ b/src/ifctester/ifctester/__main__.py
@@ -23,6 +23,7 @@ import argparse
 import ifcopenshell
 from . import ids
 from . import reporter
+from pathlib import Path
 
 parser = argparse.ArgumentParser(description="Uses an IDS to audit an IFC")
 parser.add_argument("ids", type=str, help="Path to an IDS")
@@ -33,10 +34,19 @@ parser.add_argument("--excel-safe", help="Make sure exported ODS is safely expor
 parser.add_argument("-o", "--output", help="Output file (supported for all types of reporting except Console)")
 args = parser.parse_args()
 
-specs = ids.open(args.ids)
+ids_path = Path(args.ids)
+if ids_path.suffix.lower() != ".ids":
+    raise Exception(f"Provided file is not an .ids file: '{ids_path}'.")
+
+ifc_patch = Path(args.ifc)
+if ifc_patch.suffix.lower() != ".ifc":
+    raise Exception(f"Provided file is not an .ifc file: '{ifc_patch}'.")
+
+specs = ids.open(str(ids_path))
 if args.ifc:
     start = time.time()
-    ifc = ifcopenshell.open(args.ifc)
+    ifc = ifcopenshell.open(ifc_patch)
+    assert isinstance(ifc, ifcopenshell.file)
     print("Finished loading:", time.time() - start)
     start = time.time()
     specs.validate(ifc)