diff --git a/src/grammar.ne b/src/grammar.ne
index f38efe7..50ee2e3 100644
--- a/src/grammar.ne
+++ b/src/grammar.ne
@@ -49,7 +49,8 @@
   };
 %}
 
-number -> ([0-9]:+) {% d => Number(text(d)) %}
+number
+  -> "-":? ([0-9]:? "." [0-9]:+ | [1-9] [0-9]:* | "0") {% d => Number(text(d)) %}
 
 angle -> number ("deg" | "rad") {% text %}
 
diff --git a/src/index.test.js b/src/index.test.js
index f26d4eb..fd83e8f 100644
--- a/src/index.test.js
+++ b/src/index.test.js
@@ -17,6 +17,24 @@ it('allows decimal values', () => runTest([
   ['top', '1.5'],
 ], { top: 1.5 }));
 
+it('allows decimal values in transformed values', () => runTest([
+  ['border-radius', '1.5'],
+], {
+  borderTopLeftRadius: 1.5,
+  borderTopRightRadius: 1.5,
+  borderBottomRightRadius: 1.5,
+  borderBottomLeftRadius: 1.5,
+}));
+
+it('allows negative values in transformed values', () => runTest([
+  ['border-radius', '-1.5'],
+], {
+  borderTopLeftRadius: -1.5,
+  borderTopRightRadius: -1.5,
+  borderBottomRightRadius: -1.5,
+  borderBottomLeftRadius: -1.5,
+}));
+
 it('transforms strings', () => runTest([
   ['color', 'red'],
 ], { color: 'red' }));