Index: ext/bigdecimal/bigdecimal.c
===================================================================
--- ext/bigdecimal/bigdecimal.c	(revision 29252)
+++ ext/bigdecimal/bigdecimal.c	(working copy)
@@ -308,9 +308,9 @@
   *
   * ROUND_UP:: round away from zero
   * ROUND_DOWN:: round towards zero (truncate)
-  * ROUND_HALF_UP:: round up if the appropriate digit >= 5, otherwise truncate (default)
-  * ROUND_HALF_DOWN:: round up if the appropriate digit >= 6, otherwise truncate
-  * ROUND_HALF_EVEN:: round towards the even neighbor (Banker's rounding)
+  * ROUND_HALF_UP:: round towards the nearest neighbor, unless both neighbors are equidistant, in which case round away from zero. (default)
+  * ROUND_HALF_DOWN:: round towards the nearest neighbor, unless both neighbors are equidistant, in which case round towards zero.
+  * ROUND_HALF_EVEN:: round towards the nearest neighbor, unless both neighbors are equidistant, in which case round towards the even neighbor (Banker's rounding)
   * ROUND_CEILING:: round towards positive infinity (ceil)
   * ROUND_FLOOR:: round towards negative infinity (floor)
   *
@@ -4560,7 +4560,7 @@
 {
     /* fracf: any positive digit under rounding position? */
     /* exptoadd: number of digits needed to compensate negative nf */
-    int fracf;
+    int fracf, fracf_1further;
     ssize_t n,i,ix,ioffset, exptoadd;
     BDIGIT v, shifter;
     BDIGIT div;
@@ -4588,15 +4588,14 @@
     n = (ssize_t)BASE_FIG - ioffset - 1;
     for (shifter=1,i=0; i<n; ++i) shifter *= 10;
     fracf = (v % (shifter * 10) > 0);
+    fracf_1further = ((v % shifter) > 0);
     v /= shifter;
     div = v / 10;
     v = v - div*10;
-    if (fracf == 0) {
-        for (i=ix+1; (size_t)i < y->Prec; i++) {
-            if (y->frac[i] % BASE) {
-                fracf = 1;
-                break;
-            }
+    for (i=ix+1; (size_t)i < y->Prec; i++) {
+        if (y->frac[i] % BASE) {
+            fracf = fracf_1further = 1;
+            break;
         }
     }
     memset(y->frac+ix+1, 0, (y->Prec - (ix+1)) * sizeof(BDIGIT));
@@ -4610,7 +4609,7 @@
         if (v>=5) ++div;
         break;
     case VP_ROUND_HALF_DOWN: /* Round half down  */
-        if (v>=6) ++div;
+        if (v>5 || (v == 5 && fracf_1further)) ++div;
         break;
     case VP_ROUND_CEIL: /* ceil */
         if (fracf && (VpGetSign(y)>0)) ++div;
@@ -4621,11 +4620,16 @@
     case VP_ROUND_HALF_EVEN: /* Banker's rounding */
         if (v>5) ++div;
         else if (v==5) {
-            if ((size_t)i == (BASE_FIG-1)) {
-                if (ix && (y->frac[ix-1]%2)) ++div;
+            if (fracf_1further) {
+              ++div;
             }
-	    else {
-                if (div%2) ++div;
+            else {
+                if (ioffset == 0) {
+                    if (ix && (y->frac[ix-1]%2)) ++div;
+                }
+          	    else {
+                    if (div%2) ++div;
+                }
             }
         }
         break;
Index: test/bigdecimal/test_bigdecimal.rb
===================================================================
--- test/bigdecimal/test_bigdecimal.rb	(revision 29252)
+++ test/bigdecimal/test_bigdecimal.rb	(working copy)
@@ -612,6 +612,18 @@
     assert_equal(3, x.round(0, BigDecimal::ROUND_CEILING))
     assert_equal(2, x.round(0, BigDecimal::ROUND_FLOOR))
     assert_raise(TypeError) { x.round(0, 256) }
+
+    15.times do |n|
+      x = BigDecimal.new("5#{'0'*n}1")
+      assert_equal(10**(n+2), x.round(-(n+2), BigDecimal::ROUND_HALF_DOWN))
+      assert_equal(10**(n+2), x.round(-(n+2), BigDecimal::ROUND_HALF_EVEN))
+      x = BigDecimal.new("0.5#{'0'*n}1")
+      assert_equal(1, x.round(0, BigDecimal::ROUND_HALF_DOWN))
+      assert_equal(1, x.round(0, BigDecimal::ROUND_HALF_EVEN))
+      x = BigDecimal.new("-0.5#{'0'*n}1")
+      assert_equal(-1, x.round(0, BigDecimal::ROUND_HALF_DOWN))
+      assert_equal(-1, x.round(0, BigDecimal::ROUND_HALF_EVEN))
+    end
   end
 
   def test_truncate