diff --git a/iridiumtk/reassembler/ida.py b/iridiumtk/reassembler/ida.py
index 177be65..ab8eee3 100755
--- a/iridiumtk/reassembler/ida.py
+++ b/iridiumtk/reassembler/ida.py
@@ -992,6 +992,9 @@ def gsmwrap(self,q):
 
         fchan, foff = channelize(freq)
 
+        if fchan < 0: # Can happen if frequencies are off
+            fchan += 0x2000
+
         # GSMTAP:
         #
         #struct gsmtap_hdr {