diff --git a/ansi-tests/bit-and.lsp b/ansi-tests/bit-and.lsp
index ef1e91c4cdf3a5f4281a49a945fa83c8def95cc2..df27299c4e042a6daedd0dfae00ed3d62ee212e1 100644
--- a/ansi-tests/bit-and.lsp
+++ b/ansi-tests/bit-and.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*0 2 1 2)
 
+(deftest bit-and.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-and #*01101 #*01011)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 1) bv) (%f)))
+  #*01001 #*11001 #*01001)
+
 ;;; Error tests
 
 (deftest bit-and.error.1
diff --git a/ansi-tests/bit-andc1.lsp b/ansi-tests/bit-andc1.lsp
index 67f72b38c8d9c1b103536300ce3d8e57bb43cb90..571fda87df492d5817aa2606550e1d686dd50049 100644
--- a/ansi-tests/bit-andc1.lsp
+++ b/ansi-tests/bit-andc1.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*0 2 1 2)
 
+(deftest bit-andc1.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-andc1 #*10010 #*01011)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 1) bv) (%f)))
+  #*01001 #*11001 #*01001)
+
 ;;; Error tests
 
 (deftest bit-andc1.error.1
diff --git a/ansi-tests/bit-andc2.lsp b/ansi-tests/bit-andc2.lsp
index 54b57f795242bc1821e34786005d2178d72e6f03..646ef3ec02824e0360d58cd762c78bc5e4fa6e40 100644
--- a/ansi-tests/bit-andc2.lsp
+++ b/ansi-tests/bit-andc2.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*0 2 1 2)
 
+(deftest bit-andc2.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-andc2 #*01101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 1) bv) (%f)))
+  #*01001 #*11001 #*01001)
+
 ;;; Error tests
 
 (deftest bit-andc2.error.1
diff --git a/ansi-tests/bit-eqv.lsp b/ansi-tests/bit-eqv.lsp
index b44847b7f0b2e5a006ff443143ee709a9b2d2d2a..60290002fde045861c80bfd63f05cf1de592ac4d 100644
--- a/ansi-tests/bit-eqv.lsp
+++ b/ansi-tests/bit-eqv.lsp
@@ -229,6 +229,12 @@
      x y z))
   #*1 2 1 2)
 
+(deftest bit-eqv.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-eqv #*01101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 1) bv) (%f)))
+  #*00110 #*10110 #*00110)
+
 ;;; Error tests
 
 (deftest bit-eqv.error.1
diff --git a/ansi-tests/bit-ior.lsp b/ansi-tests/bit-ior.lsp
index 87401cc0e8873f75ea24c40cd62fcc56141a5316..b213b9e42bc6f1db5e186fe79d7cd64dcb4da35f 100644
--- a/ansi-tests/bit-ior.lsp
+++ b/ansi-tests/bit-ior.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*0 2 1 2)
 
+(deftest bit-ior.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-ior #*00101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*10101 #*00101 #*10101)
+
 ;;; Error tests
 
 (deftest bit-ior.error.1
diff --git a/ansi-tests/bit-nand.lsp b/ansi-tests/bit-nand.lsp
index 07e6c071a81a5d7804fa9499b9ef130bd9e698f3..75bf5c0b35a61ae3ce3a49d542cd7021589aeea2 100644
--- a/ansi-tests/bit-nand.lsp
+++ b/ansi-tests/bit-nand.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*1 2 1 2)
 
+(deftest bit-nand.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-nand #*00101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*11011 #*01011 #*11011)
+
 ;;; Error tests
 
 (deftest bit-nand.error.1
diff --git a/ansi-tests/bit-nor.lsp b/ansi-tests/bit-nor.lsp
index 0064fd8332edba32a7f8d088764fb6d4ef849d29..866b8658559e4ed306a0ccff5d05633b1b30db85 100644
--- a/ansi-tests/bit-nor.lsp
+++ b/ansi-tests/bit-nor.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*1 2 1 2)
 
+(deftest bit-nor.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-nor #*00101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 1) bv) (%f)))
+  #*01010 #*11010 #*01010)
+
 ;;; Error tests
 
 (deftest bit-nor.error.1
diff --git a/ansi-tests/bit-not.lsp b/ansi-tests/bit-not.lsp
index 44c9832a21fc482cba01cca68138e2988090232b..a62a0192993cd96bb9a202cc179a6eb833d540f9 100644
--- a/ansi-tests/bit-not.lsp
+++ b/ansi-tests/bit-not.lsp
@@ -127,6 +127,12 @@
      i x))
   #*110010 1 1)
 
+(deftest bit-not.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-not #*00101)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*11010 #*01010 #*11010)
+
 ;;; Error tests
 
 (deftest bit-not.error.1
diff --git a/ansi-tests/bit-orc1.lsp b/ansi-tests/bit-orc1.lsp
index 33b651ad10c7a573c97ee1034f3fa33ffcb50736..49a344a5bdedc9b79c1744378e7783518ac64002 100644
--- a/ansi-tests/bit-orc1.lsp
+++ b/ansi-tests/bit-orc1.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*1 2 1 2)
 
+(deftest bit-orc1.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-orc1 #*11010 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*10101 #*00101 #*10101)
+
 ;;; Error tests
 
 (deftest bit-orc1.error.1
diff --git a/ansi-tests/bit-orc2.lsp b/ansi-tests/bit-orc2.lsp
index cbd172eb81661c51539268c002313ca3c5c9c84f..f85a5423cb7b1936bad72d1cab36f2133170667c 100644
--- a/ansi-tests/bit-orc2.lsp
+++ b/ansi-tests/bit-orc2.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*1 2 1 2)
 
+(deftest bit-orc2.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-orc2 #*00101 #*01011)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*10101 #*00101 #*10101)
+
 ;;; Error tests
 
 (deftest bit-orc2.error.1
diff --git a/ansi-tests/bit-xor.lsp b/ansi-tests/bit-xor.lsp
index 4e7955e7b22a733d9599906c173308944da1f04c..230028df4e62c0427c7aa331091796b386ab6ae7 100644
--- a/ansi-tests/bit-xor.lsp
+++ b/ansi-tests/bit-xor.lsp
@@ -228,6 +228,12 @@
      x y z))
   #*0 2 1 2)
 
+(deftest bit-xor.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (bit-xor #*00101 #*10100)))
+    (values (%f) (let ((bv (%f))) (setf (elt bv 0) 0) bv) (%f)))
+  #*10001 #*00001 #*10001)
+
 ;;; Error tests
 
 (deftest bit-xor.error.1
diff --git a/ansi-tests/coerce.lsp b/ansi-tests/coerce.lsp
index 9fb48f08af6140499990b181b5688be918ccc28a..863e8930005f1754c484c73ad2761f86f1d91fa8 100644
--- a/ansi-tests/coerce.lsp
+++ b/ansi-tests/coerce.lsp
@@ -139,6 +139,24 @@
      i a b))
   10.0f0 2 1 2)
 
+;;; Constant folding test
+;;; If the coerce call is folded to a constant, this will fail
+;;; when that constant is modified.
+
+(deftest coerce.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0)))
+	    (coerce '(1 2 3) 'vector)))
+    (values
+     (%f)
+     (let ((v (%f)))
+       (setf (aref v 0) 0)
+       v)
+     (%f)))
+  #(1 2 3)
+  #(0 2 3)
+  #(1 2 3))
+  
+
 ;;; Error tests
 
 ;;; (deftest coerce.error.1
@@ -198,4 +216,3 @@
 	  (t t)))
        (error (c) (declare (ignore c)) t))))
   t)
-
diff --git a/ansi-tests/concatenate.lsp b/ansi-tests/concatenate.lsp
index f9384490b2198af6360ba89ac403f2ca29ea246f..a98539bb5297e9168058523770e5e7faec3b5e35 100644
--- a/ansi-tests/concatenate.lsp
+++ b/ansi-tests/concatenate.lsp
@@ -287,6 +287,38 @@
      i x y z))
   "abcdefghi" 3 1 2 3)
 
+;;; Constant folding tests
+
+(deftest concatenate.fold.1
+  (flet ((%f () (declaim (optimize speed (safety 0) (space 0)))
+	     (concatenate 'list '(a b) '(c d))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  (a b c d) (z b c d) (a b c d))
+
+(deftest concatenate.fold.2
+  (flet ((%f () (declaim (optimize speed (safety 0) (space 0)))
+	     (concatenate 'vector '(a b) '(c d))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  #(a b c d) #(z b c d) #(a b c d))
+
+(deftest concatenate.fold.3
+  (flet ((%f () (declaim (optimize speed (safety 0) (space 0)))
+	     (concatenate 'bit-vector '(0 0) '(1 0 1))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*00101 #*10101 #*00101)
+
+(deftest concatenate.fold.4
+  (flet ((%f () (declaim (optimize speed (safety 0) (space 0)))
+	     (concatenate 'string "ab" "cd")))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) #\z) seq) (%f)))
+  "abcd" "zbcd" "abcd")
+
+(deftest concatenate.fold.5
+  (flet ((%f () (declaim (optimize speed (safety 0) (space 0)))
+	     (concatenate 'list '(a b c d))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  (a b c d) (z b c d) (a b c d))
+  
 ;;; Error tests
 
 (deftest concatenate.error.1
diff --git a/ansi-tests/map.lsp b/ansi-tests/map.lsp
index e29e1a06f4fe59fab5dacb9d761f61c65421acb1..40184a333ef647b9e3f6f96cfebe8d2cdc37867d 100644
--- a/ansi-tests/map.lsp
+++ b/ansi-tests/map.lsp
@@ -425,3 +425,14 @@
 	  (progn (setf d (incf i)) '(b c d)))
      i a b c d))
   ((a b)(b c)(c d)) 4 1 2 3 4)
+
+;;; Constant folding test
+
+(deftest map.fold.1
+  (let ((f (compile nil '(lambda () (declare (optimize speed (safety 0)))
+			   (map 'vector #'identity '(a b c))))))
+    (let ((v (funcall f)))
+      (setf (aref v 0) nil)
+      (values v (funcall f))))
+  #(nil b c)
+  #(a b c))
diff --git a/ansi-tests/remove-duplicates.lsp b/ansi-tests/remove-duplicates.lsp
index f1d837799ab3ce891b82548fc855166eec02e4ec..2e738a09c732d47bf3bd3467548e6904d0f88de4 100644
--- a/ansi-tests/remove-duplicates.lsp
+++ b/ansi-tests/remove-duplicates.lsp
@@ -54,6 +54,27 @@
   (delete-duplicates (list 'a 'b 'c 'd 'a 'e 'f 'd 'g) :test-not #'eql
 		     :test #'eql))
 
+;;; Const fold tests
+
+(deftest remove-duplicates.fold.1
+  (flet ((%f () (remove-duplicates '(1 2 3 3))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 0) seq) (%f)))
+  (1 2 3) (0 2 3) (1 2 3))
+
+(deftest remove-duplicates.fold.2
+  (flet ((%f () (remove-duplicates #(1 2 3 3))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 0) seq) (%f)))
+  #(1 2 3) #(0 2 3) #(1 2 3))
+
+(deftest remove-duplicates.fold.3
+  (flet ((%f () (remove-duplicates #*0011)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*01 #*11 #*01)
+
+(deftest remove-duplicates.fold.4
+  (flet ((%f () (remove-duplicates "1233")))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) #\0) seq) (%f)))
+  "123" "023" "123")
 
 ;;; Order of evaluation tests
 
diff --git a/ansi-tests/remove.lsp b/ansi-tests/remove.lsp
index db015a4966d929a0187cd3a5d940ae4fc4f09412..f8aee212ba9043b720e40f584886aa55604b4e59 100644
--- a/ansi-tests/remove.lsp
+++ b/ansi-tests/remove.lsp
@@ -461,6 +461,104 @@
   (delete #\0 (copy-seq "0001100100") :test-not #'eql :test #'eql))
 
 
+;;; Const fold tests
+
+(deftest remove.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove 'c '(a b c d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  (a b d e)
+  (z b d e)
+  (a b d e))
+
+(deftest remove.fold.2
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove 'c #(a b c d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  #(a b d e)
+  #(z b d e)
+  #(a b d e))
+
+(deftest remove.fold.3
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove 1 #*0011011001)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*00000
+  #*10000
+  #*00000)
+
+(deftest remove.fold.4
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove #\c "abcde")))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) #\z) seq) (%f)))
+  "abde"
+  "zbde"
+  "abde")
+
+(deftest remove-if.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if 'null '(a b nil d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  (a b d e)
+  (z b d e)
+  (a b d e))
+
+(deftest remove-if.fold.2
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if #'null #(a b nil d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  #(a b d e)
+  #(z b d e)
+  #(a b d e))
+
+(deftest remove-if.fold.3
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if 'plusp #*0011011001)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*00000
+  #*10000
+  #*00000)
+
+(deftest remove-if.fold.4
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if 'digit-char-p "ab0de")))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) #\z) seq) (%f)))
+  "abde"
+  "zbde"
+  "abde")
+
+(deftest remove-if-not.fold.1
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if-not #'identity '(a b nil d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  (a b d e)
+  (z b d e)
+  (a b d e))
+
+(deftest remove-if-not.fold.2
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if-not 'identity #(a b nil d e))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'z) seq) (%f)))
+  #(a b d e)
+  #(z b d e)
+  #(a b d e))
+
+(deftest remove-if-not.fold.3
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if-not #'zerop #*0011011001)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*00000
+  #*10000
+  #*00000)
+
+(deftest remove-if-not.fold.4
+  (flet ((%f () (declare (optimize speed (safety 0) (space 0)))
+	     (remove-if-not #'alpha-char-p "ab-de")))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) #\z) seq) (%f)))
+  "abde"
+  "zbde"
+  "abde")
+
 ;;; Order of evaluation tests
 
 (deftest remove.order.1
diff --git a/ansi-tests/reverse.lsp b/ansi-tests/reverse.lsp
index 2038683a6ced30bf1da631e379e198c982dd270c..96f68fa06bb29fe97825a32b179608ca38e87ac0 100644
--- a/ansi-tests/reverse.lsp
+++ b/ansi-tests/reverse.lsp
@@ -166,6 +166,28 @@
      i))
   (d c b a) 1)
 
+;;; Constant folding tests
+
+(deftest reverse.fold.1
+  (flet ((%f () (reverse '(a b c))))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 'z) seq)
+     (%f)))
+  (c b a)
+  (z b a)
+  (c b a))
+
+(deftest reverse.fold.2
+  (flet ((%f () (reverse #(a b c))))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 'z) seq)
+     (%f)))
+  #(c b a)
+  #(z b a)
+  #(c b a))
+
 ;;; Error cases
 
 (deftest reverse.error.1
diff --git a/ansi-tests/subseq.lsp b/ansi-tests/subseq.lsp
index ef78aaa89c3ffb43e865d1548b4a2ea2c354578f..793c35faa0df2fbbf89c2a3189070125177f3d86 100644
--- a/ansi-tests/subseq.lsp
+++ b/ansi-tests/subseq.lsp
@@ -281,6 +281,18 @@
      s i a b c))
   "xyz" "axyz" 3 1 2 3)
 
+;;; Constant folding
+
+(deftest subseq.fold.1
+  (flet ((%f () (subseq '(1 2 3) 0)))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 0) seq)
+     (%f)))
+  (1 2 3)
+  (0 2 3)
+  (1 2 3))
+
 ;;; Error cases
 
 (deftest subseq.error.1
diff --git a/ansi-tests/substitute-if-not.lsp b/ansi-tests/substitute-if-not.lsp
index 186c9548ba4effbfe5c665a4ffaabf984c191680..b703c0483dc473600a8b528a8c1503ca3588dbe5 100644
--- a/ansi-tests/substitute-if-not.lsp
+++ b/ansi-tests/substitute-if-not.lsp
@@ -816,6 +816,23 @@
   (substitute-if-not 'a #'zerop (list 1 2 0 3 1 0 3) :allow-other-keys nil)
   (a a 0 a a 0 a))
 
+;;; Constant folding tests
+
+(deftest substitute-if-not.fold.1
+  (flet ((%f () (substitute-if-not 'z 'identity '(a nil b))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'd) seq) (%f)))
+  (a z b) (d z b) (a z b))
+
+(deftest substitute-if-not.fold.2
+  (flet ((%f () (substitute-if-not 'z 'identity #(a nil b))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'd) seq) (%f)))
+  #(a z b) #(d z b) #(a z b))
+
+(deftest substitute-if-not.fold.3
+  (flet ((%f () (substitute-if-not 0 'zerop #*100110)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*000000 #*100000 #*000000)
+
 ;;; Error cases
 
 (deftest substitute-if-not.error.1
diff --git a/ansi-tests/substitute-if.lsp b/ansi-tests/substitute-if.lsp
index 8a031356e2164560266f590b3086b91fa93f235c..561fc957d38597375a6b519afa010d21b320c976 100644
--- a/ansi-tests/substitute-if.lsp
+++ b/ansi-tests/substitute-if.lsp
@@ -840,6 +840,23 @@
   (substitute-if 'a #'zerop (list 1 2 0 3 1 0 3) :allow-other-keys nil)
   (1 2 a 3 1 a 3))
 
+;;; Constant folding tests
+
+(deftest substitute-if.fold.1
+  (flet ((%f () (substitute-if 'z 'null '(a nil b))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'd) seq) (%f)))
+  (a z b) (d z b) (a z b))
+
+(deftest substitute-if.fold.2
+  (flet ((%f () (substitute-if 'z 'null #(a nil b))))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 'd) seq) (%f)))
+  #(a z b) #(d z b) #(a z b))
+
+(deftest substitute-if.fold.3
+  (flet ((%f () (substitute-if 0 'plusp #*100110)))
+    (values (%f) (let ((seq (%f))) (setf (elt seq 0) 1) seq) (%f)))
+  #*000000 #*100000 #*000000)
+
 ;;; Error cases
 
 (deftest substitute-if.error.1
diff --git a/ansi-tests/substitute.lsp b/ansi-tests/substitute.lsp
index f8c24e9593d16c416c57dcd4dcfd1d48828c0d88..ea0274e5eb9b6eb021d53f2a385acebb66ea8f65 100644
--- a/ansi-tests/substitute.lsp
+++ b/ansi-tests/substitute.lsp
@@ -1092,6 +1092,38 @@
   (substitute 'a 0 (list 1 2 0 3 1 0 3) :allow-other-keys nil)
   (1 2 a 3 1 a 3))
 
+;;; Constant folding tests
+
+(deftest substitute.fold.1
+  (flet ((%f () (substitute 'z 'b '(a b c))))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 'd) seq)
+     (%f)))
+  (a z c)
+  (d z c)
+  (a z c))
+
+(deftest substitute.fold.2
+  (flet ((%f () (substitute 'z 'b #(a b c))))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 'd) seq)
+     (%f)))
+  #(a z c)
+  #(d z c)
+  #(a z c))
+
+(deftest substitute.fold.3
+  (flet ((%f () (substitute 0 1 #*001101)))
+    (values
+     (%f)
+     (let ((seq (%f))) (setf (elt seq 0) 1) seq)
+     (%f)))
+  #*000000
+  #*100000
+  #*000000)
+
 ;;; Error cases
 
 (deftest substitute.error.1