diff --git a/src/code/target-thread.lisp b/src/code/target-thread.lisp
index e24efa0f7..da38ee8fa 100644
--- a/src/code/target-thread.lisp
+++ b/src/code/target-thread.lisp
@@ -551,11 +551,14 @@ won't like the effect."
   #!+sb-thread
   (let ((function (coerce function 'function)))
     (multiple-value-bind (res err)
-        (sb!unix::syscall ("interrupt_thread"
-                           system-area-pointer sb!alien:unsigned-long)
-                          thread
-                          (thread-%sap thread)
-                          (sb!kernel:get-lisp-obj-address function))
+        ;; protect against gcing just when the ub32 address is ready
+        ;; to be passed to C
+        (sb!sys::with-pinned-objects (function)
+          (sb!unix::syscall ("interrupt_thread"
+                             system-area-pointer sb!alien:unsigned-long)
+                            thread
+                            (thread-%sap thread)
+                            (sb!kernel:get-lisp-obj-address function)))
       (unless res
         (error 'interrupt-thread-error :thread thread :errno err)))))
 
diff --git a/version.lisp-expr b/version.lisp-expr
index c3ae8b242..7050b5e09 100644
--- a/version.lisp-expr
+++ b/version.lisp-expr
@@ -17,4 +17,4 @@
 ;;; checkins which aren't released. (And occasionally for internal
 ;;; versions, especially for internal versions off the main CVS
 ;;; branch, it gets hairier, e.g. "0.pre7.14.flaky4.13".)
-"0.9.3.49"
+"0.9.3.50"