From 9eb7660478991f91e11b19c0f7f5ff9aa78778b7 Mon Sep 17 00:00:00 2001
From: Dmitry Kryaklin <dmkryak@gmail.com>
Date: Mon, 20 Jul 2026 18:41:36 +0300
Subject: [PATCH] fix: do not round non-zero values down to zero

---
 src/lib/serialize.js |  8 +++++++-
 test/index.js        | 20 ++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/lib/serialize.js b/src/lib/serialize.js
index 8e4844f..15f65ae 100644
--- a/src/lib/serialize.js
+++ b/src/lib/serialize.js
@@ -15,6 +15,8 @@
  * @property {string} [calcName] Wrapper name to use when `calc()` is needed. Default `'calc'`.
  */
 
+const NOISE_FLOOR = 1e-12;
+
 /**
  * @param {number} v
  * @param {number | false} prec
@@ -25,7 +27,11 @@ function round(v, prec) {
     return v;
   }
   const m = Math.pow(10, prec);
-  return Math.round(v * m) / m;
+  const rounded = Math.round(v * m) / m;
+  if (rounded === 0 && Math.abs(v) > NOISE_FLOOR) {
+    return v < 0 ? -1 / m : 1 / m;
+  }
+  return rounded;
 }
 
 // §10.13 / §10.7.2: Infinity/NaN serialize as canonical keywords.
diff --git a/test/index.js b/test/index.js
index c165ae2..87a6f8b 100644
--- a/test/index.js
+++ b/test/index.js
@@ -382,6 +382,26 @@ test(
   testValue('calc(5/1000000)', '0.000005', { precision: 6 })
 );
 
+test(
+  'should not round a non-zero value down to zero',
+  testValue('calc(1/1000000)', '0.00001')
+);
+
+test(
+  'should not round a non-zero dimension down to zero',
+  testValue('calc(1px/1000000)', '0.00001px')
+);
+
+test(
+  'should not round a non-zero negative value down to zero',
+  testValue('calc(-1/1000000)', '-0.00001')
+);
+
+test(
+  'should keep rounding float noise to zero',
+  testValue('calc(0.1px + 0.2px - 0.3px)', '0px')
+);
+
 test(
   'should reduce browser-prefixed calc (1)',
   testValue('-webkit-calc(1px + 1px)', '2px')