diff --git a/lib/spack/llnl/util/tty/log.py b/lib/spack/llnl/util/tty/log.py
index 9b9278b73c..cff7f22dcd 100644
--- a/lib/spack/llnl/util/tty/log.py
+++ b/lib/spack/llnl/util/tty/log.py
@@ -203,8 +203,13 @@ def __exit__(self, exc_type, exception, traceback):
         # Flush the log to disk.
         sys.stdout.flush()
         sys.stderr.flush()
-        os.dup2(self._stdout, sys.stdout.fileno())
-        os.dup2(self._stderr, sys.stderr.fileno())
+        if self.directAssignment:
+            # We seem to need this only to pass test/install.py
+            sys.stdout = self._stdout
+            sys.stderr = self._stderr
+        else:
+            os.dup2(self._stdout, sys.stdout.fileno())
+            os.dup2(self._stderr, sys.stderr.fileno())
 
         # restore output options.
         color._force_color = self._force_color