diff --git a/module/ice-9/ports.scm b/module/ice-9/ports.scm
index 9774e46d2..0c4233198 100644
--- a/module/ice-9/ports.scm
+++ b/module/ice-9/ports.scm
@@ -243,7 +243,7 @@ interpret its input and output."
                         (lp buffered)
                         (values buf buffered)))))))))))))))
 
-(define (peek-byte port)
+(define-inlinable (peek-byte port)
   (let* ((buf (port-read-buffer port))
          (cur (port-buffer-cur buf)))
     (if (< cur (port-buffer-end buf))
@@ -261,85 +261,79 @@ interpret its input and output."
 (define-syntax-rule (decoding-error subr port)
   (throw 'decoding-error subr "input decoding error" EILSEQ port))
 
-(define-inlinable (peek-char-and-len/utf8 port)
+(define-inlinable (peek-char-and-len/utf8 port first-byte)
   (define (bad-utf8 len)
     (if (eq? (port-conversion-strategy port) 'substitute)
         (values #\? len)
         (decoding-error "peek-char" port)))
-  (let ((first-byte (peek-byte port)))
-    (cond
-     ((eq? first-byte the-eof-object)
-      (values first-byte 0))
-     ((< first-byte #x80)
-      (values (integer->char first-byte) 1))
-     ((<= #xc2 first-byte #xdf)
-      (call-with-values (lambda () (fill-input port 2))
-        (lambda (buf buffering)
-          (let ((bv (port-buffer-bytevector buf))
-                (cur (port-buffer-cur buf)))
-            (define (ref n)
-              (bytevector-u8-ref bv (+ cur 1)))
-            (when (or (< buffering 2)
-                      (not (= (logand (ref 1) #xc0) #x80)))
-              (bad-utf8 1))
-            (values (integer->char
-                     (logior (ash (logand first-byte #x1f) 6)
-                             (logand (ref 1) #x3f)))
-                    2)))))
-     ((= (logand first-byte #xf0) #xe0)
-      (call-with-values (lambda () (fill-input port 3))
-        (lambda (buf buffering)
-          (let ((bv (port-buffer-bytevector buf))
-                (cur (port-buffer-cur buf)))
-            (define (ref n)
-              (bytevector-u8-ref bv (+ cur 1)))
-            (when (or (< buffering 2)
-                      (not (= (logand (ref 1) #xc0) #x80))
-                      (and (eq? first-byte #xe0) (< (ref 1) #xa0))
-                      (and (eq? first-byte #xed) (< (ref 1) #x9f)))
-              (bad-utf8 1))
-            (when (or (< buffering 3)
-                      (not (= (logand (ref 2) #xc0) #x80)))
-              (bad-utf8 2))
-            (values (integer->char
-                     (logior (ash (logand first-byte #x0f) 12)
-                             (ash (logand (ref 1) #x3f) 6)
-                             (logand (ref 2) #x3f)))
-                    3)))))
-     ((<= #xf0 first-byte #xf4)
-      (call-with-values (lambda () (fill-input port 4))
-        (lambda (buf buffering)
-          (let ((bv (port-buffer-bytevector buf))
-                (cur (port-buffer-cur buf)))
-            (define (ref n)
-              (bytevector-u8-ref bv (+ cur 1)))
-            (when (or (< buffering 2)
-                      (not (= (logand (ref 1) #xc0) #x80))
-                      (and (eq? first-byte #xf0) (< (ref 1) #x90))
-                      (and (eq? first-byte #xf4) (< (ref 1) #x8f)))
-              (bad-utf8 1))
-            (when (or (< buffering 3)
-                      (not (= (logand (ref 2) #xc0) #x80)))
-              (bad-utf8 2))
-            (when (or (< buffering 4)
-                      (not (= (logand (ref 3) #xc0) #x80)))
-              (bad-utf8 3))
-            (values (integer->char
-                     (logior (ash (logand first-byte #x07) 18)
-                             (ash (logand (ref 1) #x3f) 12)
-                             (ash (logand (ref 2) #x3f) 6)
-                             (logand (ref 3) #x3f)))
-                    4)))))
-     (else
-      (bad-utf8 1)))))
+  (cond
+   ((< first-byte #x80)
+    (values (integer->char first-byte) 1))
+   ((<= #xc2 first-byte #xdf)
+    (call-with-values (lambda () (fill-input port 2))
+      (lambda (buf buffering)
+        (let ((bv (port-buffer-bytevector buf))
+              (cur (port-buffer-cur buf)))
+          (define (ref n)
+            (bytevector-u8-ref bv (+ cur 1)))
+          (when (or (< buffering 2)
+                    (not (= (logand (ref 1) #xc0) #x80)))
+            (bad-utf8 1))
+          (values (integer->char
+                   (logior (ash (logand first-byte #x1f) 6)
+                           (logand (ref 1) #x3f)))
+                  2)))))
+   ((= (logand first-byte #xf0) #xe0)
+    (call-with-values (lambda () (fill-input port 3))
+      (lambda (buf buffering)
+        (let ((bv (port-buffer-bytevector buf))
+              (cur (port-buffer-cur buf)))
+          (define (ref n)
+            (bytevector-u8-ref bv (+ cur 1)))
+          (when (or (< buffering 2)
+                    (not (= (logand (ref 1) #xc0) #x80))
+                    (and (eq? first-byte #xe0) (< (ref 1) #xa0))
+                    (and (eq? first-byte #xed) (< (ref 1) #x9f)))
+            (bad-utf8 1))
+          (when (or (< buffering 3)
+                    (not (= (logand (ref 2) #xc0) #x80)))
+            (bad-utf8 2))
+          (values (integer->char
+                   (logior (ash (logand first-byte #x0f) 12)
+                           (ash (logand (ref 1) #x3f) 6)
+                           (logand (ref 2) #x3f)))
+                  3)))))
+   ((<= #xf0 first-byte #xf4)
+    (call-with-values (lambda () (fill-input port 4))
+      (lambda (buf buffering)
+        (let ((bv (port-buffer-bytevector buf))
+              (cur (port-buffer-cur buf)))
+          (define (ref n)
+            (bytevector-u8-ref bv (+ cur 1)))
+          (when (or (< buffering 2)
+                    (not (= (logand (ref 1) #xc0) #x80))
+                    (and (eq? first-byte #xf0) (< (ref 1) #x90))
+                    (and (eq? first-byte #xf4) (< (ref 1) #x8f)))
+            (bad-utf8 1))
+          (when (or (< buffering 3)
+                    (not (= (logand (ref 2) #xc0) #x80)))
+            (bad-utf8 2))
+          (when (or (< buffering 4)
+                    (not (= (logand (ref 3) #xc0) #x80)))
+            (bad-utf8 3))
+          (values (integer->char
+                   (logior (ash (logand first-byte #x07) 18)
+                           (ash (logand (ref 1) #x3f) 12)
+                           (ash (logand (ref 2) #x3f) 6)
+                           (logand (ref 3) #x3f)))
+                  4)))))
+   (else
+    (bad-utf8 1))))
 
-(define-inlinable (peek-char-and-len/iso-8859-1 port)
-  (let ((byte-or-eof (peek-byte port)))
-    (if (eof-object? byte-or-eof)
-        (values byte-or-eof 0)
-        (values (integer->char byte-or-eof) 1))))
+(define-inlinable (peek-char-and-len/iso-8859-1 port first-byte)
+  (values (integer->char first-byte) 1))
 
-(define (peek-char-and-len/iconv port)
+(define (peek-char-and-len/iconv port first-byte)
   (define (bad-input len)
     (if (eq? (port-conversion-strategy port) 'substitute)
         (values #\? len)
@@ -362,17 +356,23 @@ interpret its input and output."
         (lp input-size))))))
 
 (define-inlinable (peek-char-and-len port)
-  (let ((enc (%port-encoding port)))
-    (call-with-values
-        (lambda ()
-          (case enc
-            ((UTF-8) (peek-char-and-len/utf8 port))
-            ((ISO-8859-1) (peek-char-and-len/iso-8859-1 port))
-            (else (peek-char-and-len/iconv port))))
-      (lambda (char len)
-        (if (port-maybe-consume-initial-byte-order-mark port char len)
-            (peek-char-and-len port)
-            (values char len))))))
+  (let ((first-byte (peek-byte port)))
+    (if (eq? first-byte the-eof-object)
+        (values first-byte 0)
+        (let ((first-byte (logand first-byte #xff)))
+          (call-with-values
+              (lambda ()
+                (case (%port-encoding port)
+                  ((UTF-8)
+                   (peek-char-and-len/utf8 port first-byte))
+                  ((ISO-8859-1)
+                   (peek-char-and-len/iso-8859-1 port first-byte))
+                  (else
+                   (peek-char-and-len/iconv port first-byte))))
+            (lambda (char len)
+              (if (port-maybe-consume-initial-byte-order-mark port char len)
+                  (peek-char-and-len port)
+                  (values char len))))))))
 
 (define (%peek-char port)
   (call-with-values (lambda () (peek-char-and-len port))