diff --git a/src/t.scm b/src/t.scm
index c5bb50f..0a78e5d 100644
--- a/src/t.scm
+++ b/src/t.scm
@@ -1262,42 +1262,40 @@
 ; Library names and library file lookup
 ;---------------------------------------------------------------------------------------------
 
-(define (listname->symbol lib)
-  (define postfix "/")
-  (define prefix "")
-  (define commons '(#\- #\< #\= #\>))
-  (define symbol-prefix "/")
-  (define number-prefix ".")
-  (define (mangle-symbol sym)
+  (define (mangle-symbol->string sym)
+    (define safe '(#\! #\$ #\- #\_ #\=))
     (let loop ([lst (string->list (symbol->string sym))] [text '()])
       (cond [(null? lst) 
              (list->string (reverse text))]
-            [(or (char-alphabetic? (car lst)) (char-numeric? (car lst)))
+            [(or (char-lower-case? (car lst)) (char-numeric? (car lst)))
              (loop (cdr lst) (cons (car lst) text))]
-            [(memv (car lst) commons)
+            [(memv (car lst) safe)
              (loop (cdr lst) (cons (car lst) text))]
-            [else
+            [else ; use % encoding for everything else
              (let* ([s (number->string (char->integer (car lst)) 16)]
                     [s (if (< (string-length s) 2) (string-append "0" s) s)]
-                    [l (cons #\% (string->list (string-upcase s)))])
+                    [l (cons #\% (string->list (string-downcase s)))])
                (loop (cdr lst) (append (reverse l) text)))])))
-  (define (mangle-number num)
-    (number->string num))
+
+(define (listname->symbol lib)
+  (define postfix "")
+  (define prefix "lib:/")
+  (define symbol-prefix "/")
+  (define number-prefix "/")
   (unless (list? lib) (x-error "invalid library name" lib))
   (let loop ([lst lib] [parts (list prefix)])
     (if (null? lst)
         (string->symbol (apply string-append (reverse (cons postfix parts))))
         (cond [(symbol? (car lst))
-               (loop (cdr lst) (cons (mangle-symbol (car lst)) (cons symbol-prefix parts)))]
+               (loop (cdr lst) (cons (mangle-symbol->string (car lst)) (cons symbol-prefix parts)))]
               [(exact-integer? (car lst))
-               (loop (cdr lst) (cons (mangle-number (car lst)) (cons number-prefix parts)))]
+               (loop (cdr lst) (cons (number->string (car lst)) (cons number-prefix parts)))]
               [else (x-error "invalid library name" lib)]))))
 
 (define (listname-segment->string s)
-  (cond [(symbol? s) (symbol->string s)]
-        [(number? s) (number->string s)]
-        [(string? s) s]
-        [else (c-error "invalid symbolic file name element" s)]))
+  (cond [(symbol? s) (mangle-symbol->string s)]
+        [(exact-integer? s) (number->string s)]
+        [else (c-error "invalid library name name element" s)]))
 
 (define modname-separator "_")
 
diff --git a/t.c b/t.c
index 685f04d..bb0b051 100644
--- a/t.c
+++ b/t.c
@@ -647,21 +647,23 @@ char *t_code[] = {
   "(y14:path-directory)[01},.2,@(y34:file-resolve-relative-to-base-path)["
   "22}.1]2}.0]1",
 
+  "P", "mangle-symbol->string",
+  "%1,#0'(l5:c!;c$;c-;c_;c=;).!0n,.2X4X2,,#0.0,.4,&2{%2.0u?{.1A8X3]2}.0aC"
+  "2,.0?{.0}{.1aC5}_1?{.1,.1ac,.1d,:1^[22}:0^,.1aA1?{.1,.1ac,.1d,:1^[22}'"
+  "(i16),.1aX8E8,'2,.1S3<?{.0,'(s1:0)S6}{.0},.0SdX2,'(c%25)c,.4,.1A8L6,.4"
+  "d,:1^[52}.!0.0^_1[22",
+
   "P", "listname->symbol",
-  "%1,,,,,,,#0#1#2#3#4#5#6'(s1:/).!0'(s0:).!1'(l4:c-;c<;c=;c>;).!2'(s1:/)"
-  ".!3'(s1:.).!4.2,&1{%1n,.1X4X2,,#0.0,:0,&2{%2.0u?{.1A8X3]2}.0aC4,.0?{.0"
-  "}{.1aC5}_1?{.1,.1ac,.1d,:1^[22}:0^,.1aA1?{.1,.1ac,.1d,:1^[22}'(i16),.1"
-  "aX8E8,'2,.1S3<?{.0,'(s1:0)S6}{.0},.0SuX2,'(c%25)c,.4,.1A8L6,.4d,:1^[52"
-  "}.!0.0^_1[12}.!5&0{%1'(i10),.1E8]1}.!6.7L0~?{${.9,'(s20:invalid librar"
-  "y name),@(y7:x-error)[02}}.1^,l1,.8,,#0.(i10),.1,.9,.(i12),.(i10),.(i1"
-  "3),.9,&7{%2.0u?{${.3,:0^cA8,@(y14:%25string-append),@(y13:apply-to-lis"
-  "t)[02}X5]2}.0aY0?{.1,:2^c,${.3a,:1^[01}c,.1d,:5^[22}.0aI0?{.1,:4^c,${."
-  "3a,:3^[01}c,.1d,:5^[22}:6,'(s20:invalid library name),@(y7:x-error)[22"
-  "}.!0.0^_1[82",
+  "%1,,,,#0#1#2#3'(s0:).!0'(s5:lib:/).!1'(s1:/).!2'(s1:/).!3.4L0~?{${.6,'"
+  "(s20:invalid library name),@(y7:x-error)[02}}.1^,l1,.5,,#0.7,.1,.8,.8,"
+  ".7,&5{%2.0u?{${.3,:0^cA8,@(y14:%25string-append),@(y13:apply-to-list)["
+  "02}X5]2}.0aY0?{.1,:1^c,${.3a,@(y21:mangle-symbol->string)[01}c,.1d,:3^"
+  "[22}.0aI0?{.1,:2^c,'(i10),.2aE8c,.1d,:3^[22}:4,'(s20:invalid library n"
+  "ame),@(y7:x-error)[22}.!0.0^_1[52",
 
   "P", "listname-segment->string",
-  "%1.0Y0?{.0X4]1}.0N0?{'(i10),.1E8]1}.0S0?{.0]1}.0,'(s34:invalid symboli"
-  "c file name element),@(y7:c-error)[12",
+  "%1.0Y0?{.0,@(y21:mangle-symbol->string)[11}.0I0?{'(i10),.1E8]1}.0,'(s3"
+  "3:invalid library name name element),@(y7:c-error)[12",
 
   "C", 0,
   "'(s1:_)@!(y17:modname-separator)",