diff --git a/lib/yaml/resolver.py b/lib/yaml/resolver.py
index 528fbc0e..301fad2a 100644
--- a/lib/yaml/resolver.py
+++ b/lib/yaml/resolver.py
@@ -176,8 +176,9 @@ class Resolver(BaseResolver):
 
 Resolver.add_implicit_resolver(
         u'tag:yaml.org,2002:float',
-        re.compile(ur'''^(?:[-+]?(?:[0-9][0-9_]*)\.[0-9_]*(?:[eE][-+][0-9]+)?
-                    |\.[0-9_]+(?:[eE][-+][0-9]+)?
+        re.compile(ur'''^(?:[-+]?(?:[0-9][0-9_]*)\.[0-9_]*(?:[eE][-+]?[0-9]+)?
+                    |[-+]?(?:[0-9][0-9_]*)(?:[eE][-+]?[0-9]+)
+                    |\.[0-9_]+(?:[eE][-+]?[0-9]+)?
                     |[-+]?[0-9][0-9_]*(?::[0-5]?[0-9])+\.[0-9_]*
                     |[-+]?\.(?:inf|Inf|INF)
                     |\.(?:nan|NaN|NAN))$''', re.X),
diff --git a/lib3/yaml/resolver.py b/lib3/yaml/resolver.py
index 02b82e73..18efe865 100644
--- a/lib3/yaml/resolver.py
+++ b/lib3/yaml/resolver.py
@@ -176,8 +176,9 @@ class Resolver(BaseResolver):
 
 Resolver.add_implicit_resolver(
         'tag:yaml.org,2002:float',
-        re.compile(r'''^(?:[-+]?(?:[0-9][0-9_]*)\.[0-9_]*(?:[eE][-+][0-9]+)?
-                    |\.[0-9_]+(?:[eE][-+][0-9]+)?
+        re.compile(r'''^(?:[-+]?(?:[0-9][0-9_]*)\.[0-9_]*(?:[eE][-+]?[0-9]+)?
+                    |[-+]?(?:[0-9][0-9_]*)(?:[eE][-+]?[0-9]+)
+                    |\.[0-9_]+(?:[eE][-+]?[0-9]+)?
                     |[-+]?[0-9][0-9_]*(?::[0-5]?[0-9])+\.[0-9_]*
                     |[-+]?\.(?:inf|Inf|INF)
                     |\.(?:nan|NaN|NAN))$''', re.X),