diff --git a/CHANGELOG b/CHANGELOG
index 2603dd4..43fbd7d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -21,6 +21,14 @@ Additions
 * Add ‘parse_version_info’ to parse a version string to a version info
   tuple.
 
+Bug Fixes
+---------
+  
+* Refine parsing to conform more strictly to SemVer 2.0.0.
+
+  SemVer 2.0.0 specification §9 forbids leading zero on identifiers in
+  the prerelease version.
+
 
 Version 2.6.0
 =============
diff --git a/semver.py b/semver.py
index 21b4d10..4b6fdb5 100644
--- a/semver.py
+++ b/semver.py
@@ -10,11 +10,24 @@ __version__ = '2.6.0'
 __author__ = 'Konstantine Rybnikov'
 __author_email__ = 'k-bx@k-bx.com'
 
-_REGEX = re.compile('^(?P<major>(?:0|[1-9][0-9]*))'
-                    '\.(?P<minor>(?:0|[1-9][0-9]*))'
-                    '\.(?P<patch>(?:0|[1-9][0-9]*))'
-                    '(\-(?P<prerelease>[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?'
-                    '(\+(?P<build>[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?$')
+_REGEX = re.compile(
+        r"""
+        ^
+        (?P<major>(?:0|[1-9][0-9]*))
+        \.
+        (?P<minor>(?:0|[1-9][0-9]*))
+        \.
+        (?P<patch>(?:0|[1-9][0-9]*))
+        (\-(?P<prerelease>
+            [1-9A-Za-z-][0-9A-Za-z-]*
+            (\.[1-9A-Za-z-][0-9A-Za-z-]*)*
+        ))?
+        (\+(?P<build>
+            [0-9A-Za-z-]+
+            (\.[0-9A-Za-z-]+)*
+        ))?
+        $
+        """, re.VERBOSE)
 
 _LAST_NUMBER = re.compile(r'(?:[^\d]*(\d+)[^\d]*)+')