diff --git a/src/runtime/ustring.scm b/src/runtime/ustring.scm
index 2cada76b3..adaf7e530 100644
--- a/src/runtime/ustring.scm
+++ b/src/runtime/ustring.scm
@@ -1962,23 +1962,25 @@ USA.
     (let ((predicate (char-matcher->predicate to-trim 'string-trimmer))
           (get-trimmed (if copy? substring string-slice)))
       (lambda (string)
-	(let ((end (string-length string)))
-	  (get-trimmed
-	   string
-	   (if (eq? where 'trailing)
+        (let* ((end (string-length string))
+               (the-start (if (eq? where 'trailing)
                               0
                               (let loop ((index 0))
                                 (if (and (fix:< index end)
                                          (predicate (string-ref string index)))
                                     (loop (fix:+ index 1))
-		     index)))
-	   (if (eq? where 'leading)
+                                    index))))
+               (the-end (if (eq? where 'leading)
                             end
                             (let loop ((index end))
                               (if (and (fix:> index 0)
                                        (predicate (string-ref string (fix:- index 1))))
                                   (loop (fix:- index 1))
-		     index)))))))))
+                                  index)))))
+          (get-trimmed
+           string
+           (min the-start the-end)
+           the-end))))))
 
 (define-deferred string-trimmer-options
   (keyword-option-parser
diff --git a/tests/runtime/test-string.scm b/tests/runtime/test-string.scm
index 44f37966a..0e0ade85a 100644
--- a/tests/runtime/test-string.scm
+++ b/tests/runtime/test-string.scm
@@ -3076,3 +3076,15 @@ USA.
 	 (#t #\x0061 #t #\x002C #t #\x002C #t #\x0061 #t)
 	 (#t #\x0061 #f #\x005F #f #\x0031 #t #\x002C #t #\x002C #t #\x0061 #t)
 	 (#t #\x0061 #f #\x005F #f #\x0061 #t #\x002C #t #\x002C #t #\x0061 #t))))
+
+(assert-string= "foo" (string-trim "foo   "))
+(assert-string= "foo" (string-trim "   foo"))
+(assert-string= "foo" (string-trim "   foo   "))
+(assert-string= "foo   " (string-trim-left "   foo   "))
+(assert-string= "   foo" (string-trim-right "   foo   "))
+(assert-string= "" (string-trim "\"\"" (char-set-invert (char-set #\"))))
+(assert-string= "" (string-trim-left "\"\"" (char-set-invert (char-set #\"))))
+(assert-string= "" (string-trim-right "\"\"" (char-set-invert (char-set #\"))))
+(assert-string= "foo" (string-trim "aaafooaaa" (char-set #\f #\o)))
+(assert-string= "fooaaa" (string-trim-left "aaafooaaa" (char-set #\f #\o)))
+(assert-string= "aaafoo" (string-trim-right "aaafooaaa" (char-set #\f #\o)))