diff --git a/runtime.c b/runtime.c
index dc244ac4..c384ccae 100644
--- a/runtime.c
+++ b/runtime.c
@@ -3167,14 +3167,14 @@ object bignum_minus_unsigned(void *data, object x, object y)
   case 0:	      /* x = y, return 0 */
     return C_fix(0);
   case -1:	      /* abs(x) < abs(y), return -(abs(y) - abs(x)) */
-    size = C_fix(C_bignum_size(y)); /* Maximum size of result is length of y. */
+    size = C_bignum_size(y); /* Maximum size of result is length of y. */
     size = y;
     y = x;
     x = size;
     break;
   case 1:	      /* abs(x) > abs(y), return abs(x) - abs(y) */
   default:
-    size = C_fix(C_bignum_size(x)); /* Maximum size of result is length of x. */
+    size = C_bignum_size(x); /* Maximum size of result is length of x. */
     break;
   }
 
diff --git a/test-bn.scm b/test-bn.scm
index 70917a9e..0b11ddcf 100644
--- a/test-bn.scm
+++ b/test-bn.scm
@@ -29,6 +29,18 @@ if(is_value_type(result)) {
   printf(\"fixnum result\\n\");
 } else if (type_of(result) == bignum2_tag) {
   printf(\"bignum result\\n\");
+}
+     return_closcall1(data, k, result); 
+     ")
+ (define-c test-minus
+   "(void *data, int argc, closure _, object k, object fx1, object fx2)"
+   " object bn1 = Cyc_int2bignum2(data, obj_obj2int(fx1));
+     object bn2 = Cyc_int2bignum2(data, obj_obj2int(fx2));
+     object result = bignum_minus_unsigned(data, bn1, bn2);
+if(is_value_type(result)) {
+  printf(\"fixnum result\\n\");
+} else if (type_of(result) == bignum2_tag) {
+  printf(\"bignum result\\n\");
 }
      return_closcall1(data, k, result); 
      ")
@@ -69,6 +81,21 @@ if(is_value_type(result)) {
 (write (test-str2bn "123454354534523454243999" 16))
 (newline)
 
+(write "subtraction")
+(newline)
+(map
+  (lambda (row)
+    (write row)
+    (newline))
+  (list
+    (test-minus 1 1)
+    (test-minus 1 2)
+    (test-minus -1 2)
+    (test-minus (- #x0FFFffff) (- #x0FFFffff))
+    (test-minus (- #x2FFFffff) (- #x2FFFffff))
+))
+(newline)
+
 (write "multiplication")
 (newline)
 (map