diff --git a/racket/src/cs/main.sps b/racket/src/cs/main.sps
index 779713031e..09b695a7c3 100644
--- a/racket/src/cs/main.sps
+++ b/racket/src/cs/main.sps
@@ -183,6 +183,7 @@
    (define exit-value 0)
    (define host-collects-dir init-collects-dir)
    (define host-config-dir init-config-dir)
+   (define addon-dir #f)
 
    (define (no-init! saw)
      (unless (saw? saw 'top)
@@ -330,6 +331,10 @@
                 (when init-library
                   (set! init-library `(lib ,lib-name)))
                 (loop rest-args))]
+             [("-A" "--addon")
+              (let-values ([(addon-path rest-args) (next-arg "addon directory" arg within-arg args)])
+                (set! addon-dir addon-path)
+                (loop rest-args))]
              [("-X" "--collects")
               (let-values ([(collects-path rest-args) (next-arg "collects path" arg within-arg args)])
                 (cond
@@ -545,6 +550,11 @@
         (let ([f (dynamic-require mod sym)])
           (f pch)))))
 
+   (let ([a (or addon-dir
+                (getenv "PLTADDONDIR"))])
+     (when a
+       (set-addon-dir! (path->complete-path a))))
+
    (when (getenv "PLT_STATS_ON_BREAK")
      (keyboard-interrupt-handler
       (let ([orig (keyboard-interrupt-handler)])
diff --git a/racket/src/io/Makefile b/racket/src/io/Makefile
index d894e3850f..8a27e93bbf 100644
--- a/racket/src/io/Makefile
+++ b/racket/src/io/Makefile
@@ -26,7 +26,8 @@ GLOBALS = --no-global \
           ++global-ok exec-file \
           ++global-ok run-file \
           ++global-ok collects-dir \
-          ++global-ok config-dir
+          ++global-ok config-dir \
+          ++global-ok addon-dir
 
 io-src: $(RKTIO_DEP)
 	$(RACO) make ../expander/bootstrap-run.rkt
diff --git a/racket/src/io/path/main.rkt b/racket/src/io/path/main.rkt
index 76ccdc0761..177fe195b2 100644
--- a/racket/src/io/path/main.rkt
+++ b/racket/src/io/path/main.rkt
@@ -60,6 +60,7 @@
          set-run-file!
          set-collects-dir!
          set-config-dir!
+         set-addon-dir!
 
          _path)
 
diff --git a/racket/src/io/path/system.rkt b/racket/src/io/path/system.rkt
index cb619bd452..b87645aba2 100644
--- a/racket/src/io/path/system.rkt
+++ b/racket/src/io/path/system.rkt
@@ -10,7 +10,8 @@
          set-exec-file!
          set-run-file!
          set-collects-dir!
-         set-config-dir!)
+         set-config-dir!
+         set-addon-dir!)
 
 (define/who (find-system-path key)
   (begin0
@@ -28,7 +29,8 @@
       [(sys-dir) (rktio-system-path who RKTIO_PATH_SYS_DIR)]
       [(pref-dir) (rktio-system-path who RKTIO_PATH_PREF_DIR)]
       [(pref-file) (rktio-system-path who RKTIO_PATH_PREF_FILE)]
-      [(addon-dir) (rktio-system-path who RKTIO_PATH_ADDON_DIR)]
+      [(addon-dir) (or addon-dir
+                       (rktio-system-path who RKTIO_PATH_ADDON_DIR))]
       [(home-dir) (rktio-system-path who RKTIO_PATH_HOME_DIR)]
       [(desk-dir) (rktio-system-path who RKTIO_PATH_DESK_DIR)]
       [(doc-dir) (rktio-system-path who RKTIO_PATH_DOC_DIR)]
@@ -56,6 +58,9 @@
 (define config-dir #f)
 (define (set-config-dir! p) (set! config-dir p))
 
+(define addon-dir #f)
+(define (set-addon-dir! p) (set! addon-dir p))
+
 (define (rktio-system-path who key)
   (start-atomic)
   (define s (rktio_system_path rktio key))