diff --git a/s/primdata.ss b/s/primdata.ss
index cf0db5e1a5..c5f96552cf 100644
--- a/s/primdata.ss
+++ b/s/primdata.ss
@@ -1515,7 +1515,7 @@
   (path-rest [sig [(pathname) -> (pathname)]] [flags true #;cp02])
   (path-root [sig [(pathname) -> (pathname)]] [flags true #;cp02])
   (phantom-bytevector? [sig [(ptr) -> (boolean)]] [flags pure mifoldable discard])
-  (phantom-bytevector-length [sig [(ptr) -> (ptr)]] [flags true])
+  (phantom-bytevector-length [sig [(ptr) -> (uptr)]] [flags true])
   (port-bol? [sig [(textual-output-port) -> (boolean)]] [flags discard])
   (port-closed? [sig [(port) -> (boolean)]] [flags discard])
   (port-file-descriptor [sig [(port) -> (ufixnum)]] [flags discard])
@@ -1596,7 +1596,7 @@
   (set-binary-port-output-index! [sig [(binary-output-port sub-index) -> (void)]] [flags true])
   (set-binary-port-output-size! [sig [(binary-output-port sub-length) -> (void)]] [flags true])
   (set-box! [sig [(box ptr) -> (void)]] [flags true])
-  (set-phantom-bytevector-length! [sig [(ptr ptr) -> (void)]] [flags true])
+  (set-phantom-bytevector-length! [sig [(ptr uptr) -> (void)]] [flags true])
   (set-port-bol! [sig [(textual-output-port ptr) -> (void)]] [flags true])
   (set-port-eof! [sig [(input-port ptr) -> (void)]] [flags true])
   (set-port-input-buffer! [sig [(input-port sub-ptr) -> (void)]] [flags true])
diff --git a/s/prims.ss b/s/prims.ss
index 30aa5f5899..2db816550a 100644
--- a/s/prims.ss
+++ b/s/prims.ss
@@ -1880,7 +1880,11 @@
 
   (set-who! make-phantom-bytevector
     (lambda (n)
-      (unless (and ($integer-64? n) (>= n 0))
+      (define addr?
+        (constant-case ptr-bits
+          [(32) $integer-32?]
+          [(64) $integer-64?]))
+      (unless (and (addr? n) (>= n 0))
         ($oops who "~s is not a valid phantom bytevector length" n))
       (let ([ph ($make-phantom-bytevector)])
         ($phantom-bytevector-adjust! ph n)
@@ -1893,8 +1897,12 @@
   
   (set-who! set-phantom-bytevector-length!
     (lambda (ph n)
+      (define addr?
+        (constant-case ptr-bits
+          [(32) $integer-32?]
+          [(64) $integer-64?]))
       (unless (phantom-bytevector? ph) ($oops who "~s is not a phantom bytevector" ph))
-      (unless (and ($integer-64? n) (>= n 0))
+      (unless (and (addr? n) (>= n 0))
         ($oops who "~s is not a valid phantom bytevector length" n))
       ($phantom-bytevector-adjust! ph n))))