diff --git a/span_marker/modeling.py b/span_marker/modeling.py
index 8f223458..57df8822 100644
--- a/span_marker/modeling.py
+++ b/span_marker/modeling.py
@@ -23,7 +23,7 @@
 
 T = TypeVar("T", bound="SpanMarkerModel")
 
-UNEXPECTED_KEYWORD_PATTERN = re.compile("\S+ got an unexpected keyword argument '([^']*)'")
+UNEXPECTED_KEYWORD_PATTERN = re.compile(r"\S+ got an unexpected keyword argument '([^']*)'")
 
 
 class SpanMarkerModel(PreTrainedModel):