diff --git a/lib/src/tokenizer.dart b/lib/src/tokenizer.dart
index 063ac34..a14e866 100644
--- a/lib/src/tokenizer.dart
+++ b/lib/src/tokenizer.dart
@@ -97,7 +97,7 @@
       case TokenChar.HASH:
         return _finishToken(TokenKind.HASH);
       case TokenChar.PLUS:
-        if (maybeEatDigit()) return finishNumber();
+        if (_nextCharsAreNumber(ch)) return finishNumber();
         return _finishToken(TokenKind.PLUS);
       case TokenChar.MINUS:
         if (inSelectorExpression || unicodeRange) {
@@ -105,7 +105,7 @@
           // not part of identifier e.g., interval value range (e.g. U+400-4ff)
           // or minus operator in selector expression.
           return _finishToken(TokenKind.MINUS);
-        } else if (maybeEatDigit()) {
+        } else if (_nextCharsAreNumber(ch)) {
           return finishNumber();
         } else if (TokenizerHelpers.isIdentifierStart(ch)) {
           return finishIdentifier();
diff --git a/lib/src/tokenizer_base.dart b/lib/src/tokenizer_base.dart
index ccdd7be..c2a448f 100644
--- a/lib/src/tokenizer_base.dart
+++ b/lib/src/tokenizer_base.dart
@@ -79,9 +79,9 @@
     }
   }
 
-  int _peekChar() {
-    if (_index < _text.length) {
-      return _text.codeUnitAt(_index);
+  int _peekChar([int offset = 0]) {
+    if (_index + offset < _text.length) {
+      return _text.codeUnitAt(_index + offset);
     } else {
       return 0;
     }
@@ -100,6 +100,17 @@
     }
   }
 
+  bool _nextCharsAreNumber(int first) {
+    if (TokenizerHelpers.isDigit(first)) return true;
+    var second = _peekChar();
+    if (first == TokenChar.DOT) return TokenizerHelpers.isDigit(second);
+    if (first == TokenChar.PLUS || first == TokenChar.MINUS) {
+      return TokenizerHelpers.isDigit(second) ||
+          (second == TokenChar.DOT && TokenizerHelpers.isDigit(_peekChar(1)));
+    }
+    return false;
+  }
+
   Token _finishToken(int kind) {
     return new Token(kind, _file.span(_startIndex, _index));
   }
diff --git a/test/declaration_test.dart b/test/declaration_test.dart
index 6452819..c0c8f53 100644
--- a/test/declaration_test.dart
+++ b/test/declaration_test.dart
@@ -170,8 +170,8 @@
   right: 300px;
   bottom: 400cm;
   border-width: 2.5mm;
-  margin-top: .5in;
-  margin-left: 5pc;
+  margin-top: -.5in;
+  margin-left: +5pc;
   margin-right: 5ex;
   margin-bottom: 5ch;
   font-size: 10pt;
@@ -208,8 +208,8 @@
   right: 300px;
   bottom: 400cm;
   border-width: 2.5mm;
-  margin-top: .5in;
-  margin-left: 5pc;
+  margin-top: -.5in;
+  margin-left: +5pc;
   margin-right: 5ex;
   margin-bottom: 5ch;
   font-size: 10pt;