diff --git a/retropath2_wrapper/RetroPath2.py b/retropath2_wrapper/RetroPath2.py
index ee78277..14e21bc 100644
--- a/retropath2_wrapper/RetroPath2.py
+++ b/retropath2_wrapper/RetroPath2.py
@@ -348,7 +348,7 @@ def check_inchi_from_file(
             #       Other (sub-)layers
             #       matches:
             #           (/.+)? --> if '/' is present, then at least one character/symbol is mandatory
-            if match('InChI=1(S)?/(([a-z|[A-Z])+\d*)+(/.+)?$', inchi) is None:
+            if match(r'InChI=1(S)?/(([a-z|[A-Z])+\d*)+(/.+)?$', inchi) is None:
                 logger.error('        {inchi} is not a valid InChI notation'.format(inchi=inchi))
                 return ''