diff --git a/src/compiler/early-c.lisp b/src/compiler/early-c.lisp
index a242ad9fe..d6de83dee 100644
--- a/src/compiler/early-c.lisp
+++ b/src/compiler/early-c.lisp
@@ -203,14 +203,27 @@ possible.")
         ;; And who knows what the host considers "simple".
         #-sb-xc-host (not simple-array)))
 
+(defun hash-list-of-symbols (list) ; or "nonexternalizably-hash-..."
+  ;; We don't emulate sb-xc:sxhash thoroughly enough to hash compound names
+  ;; (lists are rejected) but it doesn't actually matter what the hash is
+  ;; for duplicate name detection.
+  #+sb-xc-host (cl:sxhash list)
+  ;; SXHASH requires symbols whose print-names are the same to hash the same.
+  ;; That's not a requirement of the fun-name-hashset, so use SYMBOL-HASH here
+  ;; which contains 10 pseudorandom bits if 64-bit word size, fewer if 32-bit.
+  ;; If someone using 32-bit SBCL complains, we can mix in PACKAGE-ID too.
+  #-sb-xc-host
+  (named-let recurse ((x list))
+    (typecase x
+      (symbol (symbol-hash x))
+      ;; sure this could be made iterative, but the lists in question are short
+      (cons (mix (recurse (car x)) (recurse (cdr x))))
+      (t (sxhash x))))) ; nonstandard function name, oh well (string?)
+
 (defun make-fun-name-hashset ()
   (make-hashset 32
                 (lambda (a b) (or (eq a b) (and (consp a) (consp b) (equal a b))))
-                ;; We don't emulate sb-xc:sxhash thoroughly enough to hash compound names
-                ;; (lists are rejected) but it doesn't actually matter what the hash is
-                ;; for duplicate name detection.
-                #+sb-xc-host #'cl:sxhash
-                #-sb-xc-host #'sxhash))
+                #'hash-list-of-symbols))
 
 (defstruct (compilation (:constructor make-compilation
                                       (&optional msan-unpoison
diff --git a/src/pcl/vector.lisp b/src/pcl/vector.lisp
index e88ae33b7..e1baf1be3 100644
--- a/src/pcl/vector.lisp
+++ b/src/pcl/vector.lisp
@@ -50,7 +50,8 @@
 
 ;;; Used for interning parts of SLOT-NAME-LISTS, as part of
 ;;; PV-TABLE interning -- just to save space.
-(define-load-time-global *slot-name-lists* (make-hashset 64 #'list-elts-eq #'sxhash))
+(define-load-time-global *slot-name-lists*
+    (make-hashset 64 #'list-elts-eq #'sb-c::hash-list-of-symbols))
 
 ;;; Used for interning PV-TABLES, keyed by the SLOT-NAME-LISTS
 ;;; used.
diff --git a/tests/hashset.impure.lisp b/tests/hashset.impure.lisp
new file mode 100644
index 000000000..df95d30ab
--- /dev/null
+++ b/tests/hashset.impure.lisp
@@ -0,0 +1,9 @@
+(with-test (:name :many-packages) ; was blowing up in fun-name-hashset
+  (with-scratch-file (sourcefile "lisp")
+    (with-open-file (out sourcefile :direction :output)
+      (dotimes (i 1200)
+        (format out "(defpackage #:pkg~d (:use #:cl))
+(in-package #:pkg~d)
+(defun initme () ~d)~%" i i i)))
+    (with-scratch-file (fasl "fasl")
+      (compile-file sourcefile :output-file fasl))))