diff --git a/graphix/pattern.py b/graphix/pattern.py
index d045582c..13a6734b 100644
--- a/graphix/pattern.py
+++ b/graphix/pattern.py
@@ -1525,7 +1525,7 @@ def to_qasm3(self, filename):
         filename : str
             file name to export to. example: "filename.qasm"
         """
-        with Path(filename + ".qasm", "w").open(encoding="utf-8") as file:
+        with Path(filename).with_suffix(".qasm").open("w", encoding="utf-8") as file:
             file.write("// generated by graphix\n")
             file.write("OPENQASM 3;\n")
             file.write('include "stdgates.inc";\n')