diff --git a/ssf.js b/ssf.js
index 607d185..61b1ac9 100644
--- a/ssf.js
+++ b/ssf.js
@@ -310,7 +310,18 @@ function hashq(str/*:string*/)/*:string*/ {
   return o;
 }
 function rnd(val/*:number*/, d/*:number*/)/*:string*/ { var dd = Math.pow(10,d); return ""+(Math.round(val * dd)/dd); }
-function dec(val/*:number*/, d/*:number*/)/*:number*/ { return Math.round((val-Math.floor(val))*Math.pow(10,d)); }
+function dec(val/*:number*/, d/*:number*/)/*:number*/ {
+    if (d < ('' + Math.round((val-Math.floor(val))*Math.pow(10,d))).length) {
+        return 0;
+    }
+    return Math.round((val-Math.floor(val))*Math.pow(10,d));
+}
+function carry(val/*:number*/, d/*:number*/)/*:number*/ {
+    if (d < ('' + Math.round((val-Math.floor(val))*Math.pow(10,d))).length) {
+        return 1;
+    }
+    return 0;
+}
 function flr(val/*:number*/)/*:string*/ { if(val < 2147483647 && val > -2147483648) return ""+(val >= 0 ? (val|0) : (val-1|0)); return ""+Math.floor(val); }
 function write_num_flt(type/*:string*/, fmt/*:string*/, val/*:number*/)/*:string*/ {
   if(type.charCodeAt(0) === 40 && !fmt.match(closeparen)) {
@@ -342,7 +353,7 @@ function write_num_flt(type/*:string*/, fmt/*:string*/, val/*:number*/)/*:string
   }
   if((r = fmt.match(/^#,##0(\.?)$/))) return sign + commaify(pad0r(aval,0));
   if((r = fmt.match(/^#,##0\.([#0]*0)$/))) {
-    return val < 0 ? "-" + write_num_flt(type, fmt, -val) : commaify(""+(Math.floor(val))) + "." + pad0(dec(val, r[1].length),r[1].length);
+    return val < 0 ? "-" + write_num_flt(type, fmt, -val) : commaify(""+(Math.floor(val) + carry(val, r[1].length))) + "." + pad0(dec(val, r[1].length),r[1].length);
   }
   if((r = fmt.match(/^#,#*,#0/))) return write_num_flt(type,fmt.replace(/^#,#*,/,""),val);
   if((r = fmt.match(/^([0#]+)(\\?-([0#]+))+$/))) {
diff --git a/ssf.md b/ssf.md
index 89916af..3695a90 100644
--- a/ssf.md
+++ b/ssf.md
@@ -537,7 +537,18 @@ V8 has an annoying habit of deoptimizing round and floor
 
 ```
 function rnd(val/*:number*/, d/*:number*/)/*:string*/ { var dd = Math.pow(10,d); return ""+(Math.round(val * dd)/dd); }
-function dec(val/*:number*/, d/*:number*/)/*:number*/ { return Math.round((val-Math.floor(val))*Math.pow(10,d)); }
+function dec(val/*:number*/, d/*:number*/)/*:number*/ {
+	if (d < ('' + Math.round((val-Math.floor(val))*Math.pow(10,d))).length) {
+		return 0;
+	}
+	return Math.round((val-Math.floor(val))*Math.pow(10,d));
+}
+function carry(val/*:number*/, d/*:number*/)/*:number*/ {
+	if (d < ('' + Math.round((val-Math.floor(val))*Math.pow(10,d))).length) {
+		return 1;
+	}
+	return 0;
+}
 function flr(val/*:number*/)/*:string*/ { if(val < 2147483647 && val > -2147483648) return ""+(val >= 0 ? (val|0) : (val-1|0)); return ""+Math.floor(val); }
 ```
 
@@ -614,7 +625,7 @@ The next few simplifications ignore leading optional sigils (`#`):
   }
   if((r = fmt.match(/^#,##0(\.?)$/))) return sign + commaify(pad0r(aval,0));
   if((r = fmt.match(/^#,##0\.([#0]*0)$/))) {
-    return val < 0 ? "-" + write_num_flt(type, fmt, -val) : commaify(""+(Math.floor(val))) + "." + pad0(dec(val, r[1].length),r[1].length);
+    return val < 0 ? "-" + write_num_flt(type, fmt, -val) : commaify(""+(Math.floor(val) + carry(val, r[1].length))) + "." + pad0(dec(val, r[1].length),r[1].length);
   }
   if((r = fmt.match(/^#,#*,#0/))) return write_num_flt(type,fmt.replace(/^#,#*,/,""),val);
 ```
diff --git a/test/comma.tsv b/test/comma.tsv
index cc7a484..85ee283 100644
--- a/test/comma.tsv
+++ b/test/comma.tsv
@@ -1,15 +1,16 @@
-value	#.0000,,,	#.0000,,	#.0000,
-1.2345	.0000	.0000	.0012
-12.345	.0000	.0000	.0123
-123.456	.0000	.0001	.1235
-1234	.0000	.0012	1.2340
-12345	.0000	.0123	12.3450
-123456	.0001	.1235	123.4560
-1234567	.0012	1.2346	1234.5670
-12345678	.0123	12.3457	12345.6780
-123456789	.1235	123.4568	123456.7890
-1234567890	1.2346	1234.5679	1234567.8900
-12345678901	12.3457	12345.6789	12345678.9010
-123456789012	123.4568	123456.7890	123456789.0120
-4321	.0000	.0043	4.3210
-4321234	.0043	4.3212	4321.2340
+value	#.0000,,,	#.0000,,	#.0000,	#,##0.0
+0.99	.0000	.0000	.0010	1.0
+1.2345	.0000	.0000	.0012	1.2
+12.345	.0000	.0000	.0123	12.3
+123.456	.0000	.0001	.1235	123.5
+1234	.0000	.0012	1.2340	1,234.0
+12345	.0000	.0123	12.3450	12,345.0
+123456	.0001	.1235	123.4560	123,456.0
+1234567	.0012	1.2346	1234.5670	1,234,567.0
+12345678	.0123	12.3457	12345.6780	12,345,678.0
+123456789	.1235	123.4568	123456.7890	123,456,789.0
+1234567890	1.2346	1234.5679	1234567.8900	1,234,567,890.0
+12345678901	12.3457	12345.6789	12345678.9010	12,345,678,901.0
+123456789012	123.4568	123456.7890	123456789.0120	123,456,789,012.0
+4321	.0000	.0043	4.3210	4,321.0
+4321234	.0043	4.3212	4321.2340	4,321,234.0