diff --git a/django/template/base.py b/django/template/base.py
index e23420b828..31bc8c924b 100644
--- a/django/template/base.py
+++ b/django/template/base.py
@@ -250,15 +250,15 @@ class Parser(object):
                 var_node = self.create_variable_node(filter_expression)
                 self.extend_nodelist(nodelist, var_node, token)
             elif token.token_type == TOKEN_BLOCK:
-                if token.contents in parse_until:
-                    # put token back on token list so calling
-                    # code knows why it terminated
-                    self.prepend_token(token)
-                    return nodelist
                 try:
                     command = token.contents.split()[0]
                 except IndexError:
                     self.empty_block_tag(token)
+                if command in parse_until:
+                    # put token back on token list so calling
+                    # code knows why it terminated
+                    self.prepend_token(token)
+                    return nodelist
                 # execute callback function for this tag and append
                 # resulting node
                 self.enter_command(command, token)
diff --git a/django/template/loader_tags.py b/django/template/loader_tags.py
index b642765341..521df2dd8d 100644
--- a/django/template/loader_tags.py
+++ b/django/template/loader_tags.py
@@ -189,8 +189,14 @@ def do_block(parser, token):
         parser.__loaded_blocks.append(block_name)
     except AttributeError: # parser.__loaded_blocks isn't a list yet
         parser.__loaded_blocks = [block_name]
-    nodelist = parser.parse(('endblock', 'endblock %s' % block_name))
-    parser.delete_first_token()
+    nodelist = parser.parse(('endblock',))
+
+    # This check is kept for backwards-compatibility. See #3100.
+    endblock = parser.next_token()
+    acceptable_endblocks = ('endblock', 'endblock %s' % block_name)
+    if endblock.contents not in acceptable_endblocks:
+        parser.invalid_block_tag(endblock, 'endblock', acceptable_endblocks)
+
     return BlockNode(block_name, nodelist)
 
 @register.tag('extends')