diff --git a/mypy/build.py b/mypy/build.py
index 9479351daac3..c6c44fd6ead8 100644
--- a/mypy/build.py
+++ b/mypy/build.py
@@ -2961,9 +2961,7 @@ def dfs(v: str) -> Iterator[Set[str]]:
 
         for w in edges[v]:
             if w not in index:
-                # For Python >= 3.3, replace with "yield from dfs(w)"
-                for scc in dfs(w):
-                    yield scc
+                yield from dfs(w)
             elif w not in identified:
                 while index[w] < boundaries[-1]:
                     boundaries.pop()
@@ -2977,9 +2975,7 @@ def dfs(v: str) -> Iterator[Set[str]]:
 
     for v in vertices:
         if v not in index:
-            # For Python >= 3.3, replace with "yield from dfs(v)"
-            for scc in dfs(v):
-                yield scc
+            yield from dfs(v)
 
 
 def topsort(data: Dict[AbstractSet[str],
diff --git a/mypy/fastparse.py b/mypy/fastparse.py
index 7d890570519b..577da287e421 100644
--- a/mypy/fastparse.py
+++ b/mypy/fastparse.py
@@ -98,7 +98,7 @@ def ast3_parse(source: Union[str, bytes], filename: str, mode: str,
         NamedExpr = Any
         Constant = Any
 except ImportError:
-    if sys.version_info.minor > 2:
+    if sys.version_info.minor > 4:
         try:
             from typed_ast import ast35  # type: ignore
         except ImportError:
@@ -112,7 +112,7 @@ def ast3_parse(source: Union[str, bytes], filename: str, mode: str,
                   file=sys.stderr)
     else:
         print('Mypy requires the typed_ast package, which is only compatible with\n'
-              'Python 3.3 and greater.', file=sys.stderr)
+              'Python 3.5 and greater.', file=sys.stderr)
     sys.exit(1)
 
 N = TypeVar('N', bound=Node)
diff --git a/mypy/fastparse2.py b/mypy/fastparse2.py
index 016a137c50a3..40b7e6821994 100644
--- a/mypy/fastparse2.py
+++ b/mypy/fastparse2.py
@@ -60,7 +60,7 @@
     # Import ast3 from fastparse, which has special case for Python 3.8
     from mypy.fastparse import ast3, ast3_parse
 except ImportError:
-    if sys.version_info.minor > 2:
+    if sys.version_info.minor > 4:
         try:
             from typed_ast import ast35  # type: ignore
         except ImportError:
@@ -74,7 +74,7 @@
                   file=sys.stderr)
     else:
         print('Mypy requires the typed_ast package, which is only compatible with\n'
-              'Python 3.3 and greater.', file=sys.stderr)
+              'Python 3.5 and greater.', file=sys.stderr)
     sys.exit(1)
 
 N = TypeVar('N', bound=Node)
diff --git a/tox.ini b/tox.ini
index fc2604cc7f77..3c5c18262b44 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-minversion = 3.4.0
+minversion = 3.5.1
 skip_missing_interpreters = true
 envlist = py34,
           py35,