diff --git a/cryptography/hazmat/primitives/ciphers/base.py b/cryptography/hazmat/primitives/ciphers/base.py
index d1ca6d2..1da0802 100644
--- a/cryptography/hazmat/primitives/ciphers/base.py
+++ b/cryptography/hazmat/primitives/ciphers/base.py
@@ -30,30 +30,32 @@
         self._backend = backend
 
     def encryptor(self):
+        if isinstance(self.mode, interfaces.ModeWithAuthenticationTag):
+            if self.mode.tag is not None:
+                raise ValueError(
+                    "Authentication tag must be None when encrypting"
+                )
         ctx = self._backend.create_symmetric_encryption_ctx(
             self.algorithm, self.mode
         )
-        return self._wrap_ctx(ctx, True)
+        return self._wrap_ctx(ctx, encrypt=True)
 
     def decryptor(self):
+        if isinstance(self.mode, interfaces.ModeWithAuthenticationTag):
+            if self.mode.tag is None:
+                raise ValueError(
+                    "Authentication tag must be provided when decrypting"
+                )
         ctx = self._backend.create_symmetric_decryption_ctx(
             self.algorithm, self.mode
         )
-        return self._wrap_ctx(ctx, False)
+        return self._wrap_ctx(ctx, encrypt=False)
 
     def _wrap_ctx(self, ctx, encrypt):
         if isinstance(self.mode, interfaces.ModeWithAuthenticationTag):
             if encrypt:
-                if self.mode.tag is not None:
-                    raise ValueError(
-                        "Authentication tag must be None when encrypting"
-                    )
                 return _AEADEncryptionContext(ctx)
             else:
-                if self.mode.tag is None:
-                    raise ValueError(
-                        "Authentication tag must be provided when decrypting"
-                    )
                 return _AEADCipherContext(ctx)
         else:
             return _CipherContext(ctx)