diff --git a/cctk/parse_gaussian.py b/cctk/parse_gaussian.py
index e549a3b..f7b4f77 100644
--- a/cctk/parse_gaussian.py
+++ b/cctk/parse_gaussian.py
@@ -929,6 +929,9 @@ def parse_modes(freq_block, num_atoms, hpmodes=False):
     force_ks = list()
     displacements = list()
 
+    if len(freq_block) == 0:
+        return None
+
     chunks = freq_block[0].split("Freq")
 
     if hpmodes: