diff --git a/src/ansible_compat/runtime.py b/src/ansible_compat/runtime.py
index 31f95666..a7b9acab 100644
--- a/src/ansible_compat/runtime.py
+++ b/src/ansible_compat/runtime.py
@@ -922,7 +922,8 @@ def _update_env(self, varname: str, value: list[str], default: str = "") -> None
             return
         orig_value = self.environ.get(varname, default)
         if orig_value:
-            value = [*value, *orig_value.split(":")]
+            # we just want to avoid repeating the same entries, but order is important
+            value = list(dict.fromkeys([*value, *orig_value.split(":")]))
         value_str = ":".join(value)
         if value_str != self.environ.get(varname, ""):
             self.environ[varname] = value_str