diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index dd49cf15f3..61eff18869 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -959,6 +959,7 @@ (define* (process-substitution store-item destination
                                       progress)))
       ;; Unpack the Nar at INPUT into DESTINATION.
       (restore-file input destination)
+      (close-port input)
 
       ;; Skip a line after what 'progress-proc' printed, and another one to
       ;; visually separate substitutions.