diff --git a/opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py b/opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py
index 912675f1b7..68ef972d02 100644
--- a/opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py
+++ b/opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py
@@ -29,7 +29,7 @@
 def initialize():
     # prevents auto-instrumentation of subprocesses if code execs another python process
     environ["PYTHONPATH"] = _python_path_without_directory(
-        environ["PYTHONPATH"], dirname(abspath(__file__)), pathsep
+        environ.get("PYTHONPATH", ""), dirname(abspath(__file__)), pathsep
     )
 
     try: