diff --git a/pyodide_build/pywasmcross.py b/pyodide_build/pywasmcross.py
index 46d5ab5d6..da9f94949 100755
--- a/pyodide_build/pywasmcross.py
+++ b/pyodide_build/pywasmcross.py
@@ -108,7 +108,7 @@ def handle_command(line, args):
     for arg in line:
         if r'/file.c' in arg or '_configtest' in arg:
             return
-        if re.match('/tmp/.*/source\.[bco]+', arg):
+        if re.match(r'/tmp/.*/source\.[bco]+', arg):
             return
         if arg == '-print-multiarch':
             return